Definitely could see Zelda and Pokemon having big things planned for next year, especially since next year is their only series anniversary during the Switch era.
For Zelda, I do agree that WWHD and TPHD arrive on Switch. I also think SSHD should be included, with the 3 being bundled similar to 3D All-Stars. Unlike other Wii U ports, I don't see WWHD and TPHD adding anything on Switch, which is fine. They had new things added when brought to Wii U initially. Maybe the new thing could be them being bundled and also with SS as part of the bundle.
Of course, I see BOTW 2 releasing next year. Hoping for it to be in the early part of that year, but I could see it being later in the year unfortunately. I could also see Nintendo releasing a version of BOTW that includes all the DLC (and subsequently phasing out the non-DLC version of BOTW, while still keeping the DLC available on the eShop for those who previously bought vanilla BOTW, but never got the DLC).
For Pokemon, I anticipate, we will see DP remakes (and they'd probably be announced around May/June. like most remakes and follow-ups). Like my idea for BOTW, I can see Nintendo doing the same thing with SWSH. We also have New Snap on the way and I wonder if Detective Pikachu will make it out in 2021 as well. Admittedly, I don't have many other ideas for new games. Most of my Pokemon wants are more remakes (Explorers, Colosseum/XD). I don't expect a big combo pack of older main series games, like what was done with Mario. I could see Gen 1 and 2 comin to NSO, assuming we get Game Boy/Game Boy Color games soon (which is probably more likely than N64 games in my opinion).
Next year is also the 35th anniversary of Metroid & Kid Icarus! I don't expect anything, but seeing the Prime Trilogy and KI: Uprising in HD on Switch would be awesome.
EDIT: Also, next month is Animal Crossing's 20th anniversary! I do think they'll have some cool things planned for ACNH, considering how much of a sales behemoth that game is. I wonder if they will go by the N64 launch or the GCN launch. Both are 2001, but I wonder which date they'd use to kick off a potential celebration.