A few thoughts from my perspective. Some things I really like about X-plane 11. The landscape is much more realistic than FSX and from the screenshots i have seen P3D v3 or 4. Airports out of the box, look a lot more like the airports I have seen than FSX. OK, what will FS2020 look like, it may be even better or it may model generic farmland like FSX. I have not seen any screenshots out in the world I fly from FS2020 so i don't have any real opinion, but X-plane is a big improvement over FSX in that regard.
My BIG complaint with X-plane 11 is the lack of real options for quality aircraft, in freeware. Many freeware models are visually amateurish and many just don't fly the way I expect. The autopilot in X-plane is very different than in FSX, An example, the free Airbus A350 when set to a flight level of 36,000 feet, will just keep climbing on out past 40,000 ft. Even negative vs settings don't stop the climb. This morning, a small AI aircraft was sitting nose down in the traffic way of Menorca Airport, blocking traffic. There are just too many unexpected malfunctions and oddities in X-plane. I hope FS2020 will get that kind of thing solved before release.
Now what I expect to be a problem with FS2020. Software in general has become more intrusive and sends out more information than I prefer. Will FS2020 be a vehicle to collect more data? Will it be a short subscription service, requiring monthly "investment". Will the community be able to support FS2020 like FS9 & FSX, with a massive variety of quality free models and gorgeous payware aircraft? Will the flight model be configurable and adaptable? We don't know any of that yet, just that big cities look fantastic.
One more thing with X-plane 11, it does need computer power to exploit it. My frame rates are quite good in the places I fly, but the fan speeds are greater than FSX or other software I run. If I didn't have a modern computer, I don't think it would run well.
Caveat, I am old enough to remember chastising a then prominent participant on this forum who was complaining about going to FS2000 and the learning curve required. I admonished him to be patient, that the improvement more than justified the reaclimation. I suspect FS2020 will be a similar step forward.