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.
Alphadreams (Mario & Luigi) and Atlus's Etrian Odyssey teams (EO Nexus and Persona Q2 were originally released in 2018) are obvious examples. Nintendo's internal teams that released games in 2017 (Breath of the Wild, MK8D/ARMS, Splatoon 2 and Super Mario Odyssey) will have had three years of development for 2020 titles, so the second wave of major Switch titles is drawing closer. Of course Nintendo will have more games than just Animal Crossing and BotW2 to release in 2020, but they have been in no hurry to make announcements because the rest of 2019 is packed. Bayonetta scores well with critics and the third game should be coming in 2020.
Given that it took most third parties until early 2018 to realize that Switch is a winner, more content from Japanese third parties can be expected in 2020. It's common that games get announced by them only several months before release, so not knowing at this point in time doesn't rule out that 2020 will be a good year.