I mean obviously Zelda should be the next collection, with Zelda's 35th anniversary coming up in February, and there already being rumors that they'll do something with it like they are doing with Mario. I'm assuming they aren't gonna put 5 Zeldas in one package, since they couldn't even be bothered to put both Galaxy's in the same collection, so I'm guessing Zelda collection of OoT, MM, WW, and then maybe TP HD and SS HD sold individually or as a second full price collection.

Also Metroid Prime Trilogy of course.

Pikmin Trilogy would have been nice instead of just 3 Deluxe.

How about a Mario Kart Collection haha. Super, 64, Double Dash, and Wii all in one Collection, with online play and HD resolution...I just miss Double Dash.

Donkey Kong is just a much less popular franchise. Those aren't major sellers, and the best ones were on SNES, so they will all eventually be available on Switch Online. DK64 sucked and there is no need to ever revisit it, and Switch already has a port of the last one, so the only one of the modern games (DKC and after) that is missing is the Wii game, well I haven't played Jungle Beat but that doesn't lend itself as well to normal controls since I am guessing the fun of that was playing on the bongos. It would have been nice if Nintendo had thrown in the Wii DKC in the cart with Tropical Freeze, that way upping the price to $60 would have been more justified. But yeah I don't really feel the need for a Donkey Kong collection at all. Maybe just a collection of the old school pre-DKC games on the eshop for $20 or something, but I don't really think thats a big deal.

Zelda and Metroid in 2021. Donkey Kong Country trilogy and 64 would be awesome. Star Fox with all Star Fox games including Adventures would be great, I had started Adventures on the Gamecube but didn't get too far into it. Earthbound would be great. Not Nintendo but a compilations of Square games like Chrono Trigger, Secret of Evermore type games would be awesome as well.

The one I want most is a Metroid Prime Trilogy port. Well, I would want Zelda just as much, but I think with a Zelda collection they'd end up only packing in two games. If it was something like Wind Waker HD, Twillight Princess HD, and a Skyward Sword HD that would be super cool, but it won't be. At best it will be a Wind Waker HD and Twilight Princess HD double pack (and I say best because whilst OoT and MM are arguably more beloved, I personally already have them immediately accessible on the 3DS). You just know Skyward Sword would be "too generous", which sucks because given how divisive it is I *really* don't want to have to pay $60 just to try it when or if it eventually gets a Switch port. 

That's just factually inaccurate compared to other games you listed like Metroid Prime or Pikmin. Donkey Kong is less popular now, in large part, because Nintendo made it less popular now. The SNES games sold 9m, 5m, and 3.5m respectively, making every entry part of the top 10 best selling SNES games. Donkey Kong 64 sold 5m. Returns on the Wii alone sold a gigantic 6.5m with the 3DS port selling 1.5m as of 2014, almost as much as Tropical Freeze. Yea, the decline in popularity that Donkey Kong had on the Wii U was pretty big, arguably bigger than other franchises (it's a little hard to gauge when a lot of Wii to Wii U titles either didn't get a Wii U sequel, or had abnormalities affecting comparisons like Galaxy getting two entries or BOTW not launching until the Wii U was already dead), but that's not really a testament to the series popularity. It is one of their biggest franchises and would probably sell as well as Luigi's Mansion 3 if it had an ambitious new entry, the series even has potential to be bigger than LM I'd say given it started at much healthier sales. 

A Zelda Collection is the most likely to happen for its 35th anniversary. Probably including Ocarina of Time, Wind Waker HD and Twilight Princess HD. And now that we mention these two titles, I must say that it will be hilarious to see how, if they ever come to the Switch, they will be inferior versions to their Wii U counterparts xD

As for which collection I would like the most to come true... I would love to see a Xenoblade Chronicles Collection. It would be so fucking epic. However... size might be a problem. Both Xenoblade Chronicles: Definitive Edition and Xenoblade Chronicles 2 are 14 GB each and Xenoblade Chronicles X weights a whopping (for Nintendo standards) 20 GB. 58 GB in total. If we add Torna, more than 62 GB. I don't know if Nintendo has carts as big... and even if they do... I don't think they would be willing to use them on Xenoblade.

I would also wet my pants with a Golden Sun Collection. But I doubt that will ever be done. If anything, they should reboot the franchise in some way. But Nintendo has completely forgot about the franchise and Camelot has become a Mario Sports machine. I don't think they even have the creative power to create a new Golden Sun game.

A Golden Sun dual pack would be easy enough to do.

Zelda's already getting enough love. Give me Metroid (or just bring back MP Trilogy i'll be happy)

MOTHER! AKA Earthbound!

DKC 1,2,3 + Tropical Freeze

Paper Mario Collection should be a no brainer, at least the first three. And they should do what they've done in some cases with other ports and add additional content (like Luigi's side quest in TTYD, I would die).

What I want most is a classic Zelda collection.  Take the 3 NES/SNES Zeldas and give them the Link's Awakening treatment and package them together in one box.  If they include extra content with it then I definitely wouldn't object.