I understand why A2A have left FSX and P3D behind. In any discussion about "abandonment", we need to face the reality that FSX and anything based on it is sixteen years old. In computer terms, that's ancient to the point of being antediluvian. Lockheed Martin will have to keep up with the competition if they want to maintain market share, and therefore, the viability of any third party product support.
The next question then posed is one of viability for L-M. Is it worth it for them to continue, given that they may not be in the business of computer gaming and flight simulation? If they have valued customers such as the military or flight schools who require a different type of flight sim, then perhaps they are in that business. I can't provide an answer for that.
I've kept my P3D (V4.5) installation because of both instability issues with MSFS and an at present lack of A2A content for MSFS. Add on better mesh, weather and scenery and it's still an acceptable sim. But if we use predominantly GA aircraft, such as A2A's upcoming Comanche, then MSFS becomes the sim of choice. Perhaps X-Plane 12 too, but I have no experience of X-Plane to be able to comment. Running military jets around at low altitude also become more enjoyable and involving. Let's face it, even Tubeliners are better in MSFS as all planes operate at low altitudes at some points in each flight. So if or when I resolve the instability issues with MSFS, and also when A2A have more releases for that sim, then my use of P3D will diminish. I'm disappointed that A2A never brought the P-47 up to P3D standards, but I don't have FSX on my PC just for one plane.
I'd like to hope that A2A will bring all their present FSX/P3D catalogue on to the MSFS platform eventually, but I think the market will also dictate that they develop other newer products too. Given their revisions to the Accu-Sim module, I can't say how easy redoing old product will be, but previous comments from them would suggest it's not out of the bounds of possibility. However, already I've read dismissive comment elsewhere about "port overs", but people will vote with their money. That will determine what of the present catalogue becomes available for MSFS and possibly X-Plane. Personally, I'm hoping for a mix of the two for a while. One old, one new.
So what would I spend my money on, from the present catalogue? In order, Comanche, Spitfire, Cessna 182, T-6 Texan, Bonanza, P-40, Cherokee, Cub, Connie. But I'd also be a day one buyer of the P-47 if A2A decided to release that gorgeous plane for MSFS. As I would for any GA twin from A2A.