From what they’ve said, it seems to me they’re
- concerned about the size of the client. I’ve nearly filled my 1TB SSD and the only thing on it is MSFS.
- Want to continue to easily update the sim. Hopefully that’s a lot easier on their side, rather than sending all that data to us every couple of months, given all the complaints we see here. Granted, any forum is going to have more complainers than happy people responding, but, still, I think there’s some major advantages there.
I think they said the dataset they have for the world is in multiple petabytes?
Overall, it seems they feel we’ll be getting better performance with the new datamodel. I feel bad for the people who don’t have good bandwidth or can’t afford it. I imagine they’ve been studying the data they get from their telemetry, and realized the market for the advantages of this new system are greater than the disadvantages it will be for some. Be that as it may, it sounds like they’ll be supporting 2020 for some years to come, albeit at a slower pace of updates.
Not to mention, there’s always FSX on steam or P3D! 
I just fired it up the other day 
With stuff like Ultimate Terrain and many other addons, it’s not half bad and even runs well at 4K. And has been noted, even though it’s not as sophisticated as MSFS, developers were able to manage flight models easier and better than they can in MSFS. Even 3 years later, MSFS is still a baby compared to FSX. Clearly, the ceiling is WAYYYYY higher for MSFS in terms of functionality we’ll get in the future, for those with limited cash and hardware, it’s not the end of the world. (Yeah, I tried X-plane, like 
products, I just never could get on with it, and, yes, I have my pilots license and use it.)