Interesting that the most responders are P3DV4 with FSX second, understandable.

MarkOz's point about add-ons is very pertinent. Besides Captain Sim products which have yet to be upgraded to V4 I have a collection of aircraft some special FSX native models and some that were FS9 to FSX portovers (which I have spent a lot of time working on, textures, panels, gauges etc to get them to where I wanted them to have authentic visuals, panels and sounds), and they cannot be moved over to V4 because of their 32 bit architecture. This also applies to scenery addons because I have a lot of stuff for the Pacific and Japan that will also be in the same non carry over category. As well the developers who did these will not rebuild them for V4 or similar and therefore nobody in the foreseeable future will redo these models particular the Jens Kristensen flying boats. This is a major stop point for any adoption of V4 no matter how much better it really may be.

Now as for FSX well, I  run a Win7 system and with the various tinkering I have done over the years (basically respecting the 32bit architecture and limitations) I have it running basically trouble free with no OOM's or crashes. I am not really interested in moving across to Win10 either when Win7 works fine and apart from FSX has more computing capacity than I would ever use for anything else and I am also running some legacy programs on Win7 that will not run on Win10 and those programs (Lotus) are still better than anything else around for what I use them for. So a major PC upgrade is a luxury buy and technically unnecessary especially when in my household everybody else prefers the IPAD - Android world to do stuff which is not insignificant.

And I guess that is the situation that anybody who runs a business making and developing stuff in this universe of flight sim will face, the serious fragmentation of the market by these changes.