Meh. PS5/XB2 will be easy enough to develop for after the PS4/XBO. Backwards compatibility for both will help also. Expect the transition to be a lot smoother than PS2 to PS3 and PS3 to PS4.
I'm also expecting a much smoother transition from PS4->PS5, than from PS3->PS4.
I agree with X86 having potential to speed the next generation's output of games up. But how would backwards compatibility increase the output of games for PS5/XB2?
Considering that 2020 is the first year where certain former 3DS developers (both first and third party) will put out Switch games, the OP's logic falls flat. 2020 is also the year where developers who put out Switch games in 2017 or the first half of 2018 can have their next game ready. Then you have indie developers whose output isn't tied to console generations because they simply support what's out there.
PlayStation and Xbox will go through a transition, but even if that somehow gets completely botched, there will still be plenty of great games released because Switch is hitting its stride.
What are these 3DS devs? SMTV has gone dark for a long time, and Atlus' last Nintendo console game (Tokyo Mirage Sessions) was a very late gen release. All I can think of for 2020 3DS devs would be YW4, but that's already out in Japan. I give it 75% odds that BotW2 releases in 2020. But what else is there? Nothing has really been announced yet.
If indie devs went ahead and kept up the same pace it wouldn't save 2020 from having fewer games overall. They'd have to increase their output by quite a bit in order to keep the games flowing in an absence of larger devs. I'm not sure how much the indie output has grown over the years though. For all I know, they are still growing by leaps and bounds. I haven't bothered to look into it yet. Pinning down release dates for indie games is a bit of a hassle. You have to find out which version of the game launched first, vs just compiling a list on gamerankings for non-Indie games. I guess I'll do the research on that later today though.