Loved this review, I think you sum-up everything that needs to take into account when buying your next simulation, I also think you were spot on when you described the current feeling is MSFS as hollow, it is a shiny but hollow experience and I also agree that not for long.
Like you I think that MSFS is still in release candidate stage and like the release date of XP11 it will take few months until it will be stabilized and then some more to be mature.
The order of new features I would like X-Plane to introduce in X-Plane 12 are (my opinion):
Weather - this is the first thing you meet when you fly and need to cope with.
Scenery - I fly mostly in VR and the patch work is obvious although not a show stopper.
SDK & UI - I would love if X-Plane would have a better and modern set of SDK and UI widgets for developers, I even think MSFS uses an external UI library for the developers mode (although it is my assumption based on a video I saw - check 31:00min), I think they are using something like ImGUI, and if MSFS with all their knowledge and UI arsenal used such library, why not LR embracing it too at least their developers will have a default standard UI to work with.
ATC - mehh, I liked the simple ATC in MSFS, you don't need to think to much and you can do some action manually before it did it for you. I don't think that on-line simmers will replace online ATC to A.I one (maybe in XP 14 ?)
Let's see what Austin is brewing, we know he is working on a new weather engine which is great, the question is how the visuals will look, and I don't mind not having 3D clouds, really, as long it is fast and look like volumetric I can leave with it for another cycle.
For now, I stopped flying the beautiful MSFS2020, I think I had enough of it right now, I'll come back to it in few weeks or months.