I am not that sure that Slon will be fully done (at least in the next 10 years) instead of just a modernisation of the An-124, which could be start with D-18TM and later with more powerful engines (like PD-28 or PD-30) and other improvements (and some of the preliminary work done on the Slon could also be retrofitted to the An-124M).
I think being able to produce parts and keep An-124s operating make sense but there really is no future for the D-18TM engine in Russian service and therefore no need for replacement types like the PD-28 or PD-30 when they are actually going to go ahead with the PD-35.
I would say a PD-28 or PD-30 would make sense for a new An-124 in the 150 to 160 ton payload class and perhaps a twin engined Il-106 type with two PD-28/30 engines in the gap between the Il-476 at 60 tons and the An-124 at 150-160 tons, but as they are making the PD-35 I would say an Il-106 in the 100-110 ton payload capacity class and an aircraft with four PD-35s in the 180 ton payload class makes an upgraded An-124 with upgraded old DT-18M engines a bit redundant.
The Slon does not need to be some revolutionary super new wonder plane... a further evolution of systems and equipment they are upgrading the An-124 together with the new PD-35 engines and the Slon should be just fine... and in fact the Il-106 avionics and systems likely wont be a lot different either because they are all essentially large long range transports in different payload weight classes.
None of them needs to be supersonic or anything.
The use of light modern materials and clever well tested and evaluated design solutions and they should end up with two good solid aircraft that will last 40 years or more and the An-124s can be used till they wear out too... or could be sold to foreign partners perhaps.
By 2027 anyway the war in Ukraine will be long finished and the name Antonov will belong again to Russia.
Pretty sure Antonov is dead and will not be making any more aircraft ever again.
They are not keeping the An-2 designation for the Siberian upgrade, so I rather doubt they will keep any Antonov designations moving forward.
Equally a bit of pride will return and superjet and MS-21 will get their proper design codes too I hope.
It could be either combined with the Ilyushin design bureau or a new design office can be opened in Novosibirsk (which will start by being responsible of An-124M and of An-2M).
Honestly I understand them putting DT-18 engines back into production to keep the existing An-124s viable for the next decade or two, but I wouldn't make any more.
The factory that could make An-124s should make a couple of Il-106 prototypes with a few test PD-35 engines when they are ready and then get the Il-106 into production as soon as possible.
It is essentially an An-22 replacement which was a valuable and popular aircraft and would likely be used in large numbers as an essentially C-5 galaxy equivalent aircraft, and of course once you have the PD-35s in serial production you can start looking at Slon being made in the same factory.
Ilyushin and Antonov can coexist in Russia without problems in the same way MiG and Sukhoi coexists.
They probably could but they really don't need the bureaucracy of another aircraft designer based on smoke and mirrors... most of Antonovs designers and engineers have likely run to the west to work for Boeing or Airbus. The ones that remain couldn't be trusted together as a group... split them up and watch them like hawks.
The assembly plants will be anyway be shared between Ilyushin, Tupulev, Yakovlev, Antonov etc. (like it was in the soviet union) and will not belong to a design bureau.
They certainly will but the big plants for making big aircraft will be not doing very much so perhaps some might be repurposed to make Tu-214s while making a few prototype Il-106s for testing so that it is useful.
As far as the Il-106, it is important, but if they can start producing new An-124 from 2027 it will be delayed to at least 2035,
It would make more sense to make four Il-106 prototypes and get some serious testing done than waste time making stopgap planes like the Antonov.
in order to assign resources to something else (like new il-96 twin engine derivative or the An-12 replacement, if the Tu-330 is rejected)
It sounds like they are going to make Il-96s aircraft at a low rate and the Tu-330s are unlikely to start in the next 5 years, so getting these plants to start work on their next new transport plane makes sense unless they could convert them to making Il-476 and Il-276 types for a couple of years to boost numbers.
As far as an eventual PD-24, possibly it will be needed for civilian aviation:
Not convinced it is a gap that needs to be filled. The PD-35 makes sense, and the D-18TM could be a place filler for existing types.
Any new type that might use a PD-24 could be made bigger and longer ranged and use the PD-35 instead.
In 2015 it was mentioned that a possible development would be to have longer models of the MC-21, like MC-21-500 and MC-21-600, which will require engines with takeoff thrust of 20-25 tons.
It is hard enough to predict the future but for the moment I would say the places Russian airlines are allowed to fly means they don't need an enormous expansion of aircraft types and versions any time soon.
Right now replacing foreign types is the priority.
Much like you have 140 kN (PS-90A-76), 160 kN (PS-90A), 171 kN (PS-90A1) engines. You could have 280 kN (PD-28), 320 kN (PD-32), 342 kN (PD-35) engines.
That would make more sense if they had aircraft ready to go that could benefit from those different thrust options, but I would say the Il-106 and the Slon really only make sense with 35 ton thrust engines, and the 23 ton thrust requirement is temporary and already sorted it seems to me.
First of all Rolls-Royce and GE have a long experience on making engines for large aircrafts so making a new engine of this class for them is easier than it is being for Russia.
Many GE and R-R new models are just an evolution of a previous engine model.
The PD series of engines are supposed to be a modular family of engines that allows engines in different thrust ratings to be developed quickly and easily without having to start from scratch each time with a new design.
Having said that things don't always go exactly to plan every time.
So the intention could be to save time not properly designing different engines and hoping one size fits all, but the risk could be also that at the last moment it is realised that at least one of the engine version is oversized for its needed thrust while another is undersized and its core will need to run hotter and faster to meet the thrust target, causing an early deterioration.
So you will need also to do a new redesign and new development testing later, causing additional delays and much increased costs.
They wanted a PD-35 and the planes they are planning are designed around the number 35, so it would make sense for them to develop the PD-35 without making other similar engine types for the moment until the PD-35 is ready for serial production and then they can look at what else they might need that would be useful.
The Slon and Il-106 class transports are what they are needing and that is the engine they are making.
It is important to have the requirements and needed targets clear from the beginning, otherwise it will happen something like the original Ivan gren ship, where the customer changes the requirements many times already even after build started.
To be fair the Ivan Gren was a river boat they thought they could scale up to be a landing ship... the current iteration is a significant redesign but potentially could be applied to other riverboats for a successful design in the future.