So, I've been thinking about which 1st party franchises Nintendo cares about and which ones might be in danger of being cut in the next game.
So I've put them into different groups.
Flagship Franchises:
Super Mario
Donkey Kong
The Legend of Zelda
Pokemon
Animal Crossing
Mii (and associated franchises like Tomodacchi Life, Pilotwings, etc)
These are Nintendo's big money makers. Cutting these franchises would be utter suicide and each franchise will continue to get a lot of love, care and attention.
Smaller Mainstay Franchises:
Metroid
Yoshi
Kirby
Fire Emblem
Wario Ware
Pikmin
These are franchises that have proven their worth. They make a profit and have a lot of fans, but they aren't as huge as the flagship franchises. These franchises are incredibly safe. They make take breaks, but they usually aren't for very long and Nintendo knows there's still starpower behind the IP. I don't see any getting cut unless the roster is absolutely gutted.
Rising Stars
Xenoblade Chronicles
Splatoon
ARMS
These franchises are all successful so far, but they are newer franchises. That said, if their success continues, then I think all three will either go into Flagship (Splatoon) or Smaller Mainstay (Xenoblade Chronicles and ARMS). At this point in time, all three are pretty darn safe (especially Splatoon), but anything can happen, which brings us to...
Grandfathered In
Star Fox
F-Zero
Earthbound
These series aren't doing too well. All three are either dead or on life support and are way past their glory days. That said, even if Nintendo doesn't give them much care or attention, they are still remembered fondly and are given rereleases and cameos. Even still, I doubt they'd be included in Smash nowadays. Its a good thing all three franchises are already Smash staples. They're a part of Smash's identity at this point, so they're safe.
Retros
Ice Climber
Game & Watch
R.O.B.
Duck Hunt
These franchises got included through different circumstances. It's hard to gauge what will happen with these ones. Nintendo doesn't care about them outside of cameos and historical contexts, but they're all meant to be retro throwbacks. I can see these guys being low priority with only Game & Watch escaping that due to being grandfathered in.
The Awkward Spot
Kid Icarus
Wii Fit
Punch Out!!
Okay so... these franchises are in a spot where I actually think they may be in trouble. All three have... just kind of disappeared. Kid Icarus hasn't seen anything except rereleases since the early 3DS. Wii Fit may be eternally stuck to the Wii brand and Punch Out!! hasn't gotten anything new since... 2009. What's really confusing is that these franchises aren't unpopular or struggling. All three sold well, have a fair amount of brand power and have a lot of fans. Still, their apparent lack of interest may just be... that. Nintendo may just not be that interested in the IP outside of owning it and putting their characters in Smash. I can see Kid Icarus and Punch Out!! scramble their way out of this pit with a big new game but... Wii Fit might be in trouble. Unless Ring Fit Adventure and Wii Fit merge somehow, I don't see anymore Wii Fit games coming out. Wii Fit may go the way of Star Fox and F-Zero and... Wii Fit Trainer hasn't been grandfathered in like Fox, Falco and Captain Falcon. That said, there's still more reason to keep Wii Fit Trainer in Smash then not. They're just probably low priority at this point.
But what about new first party IPs in Smash? Well, unless something major happens, I think we have the majority of first party IPs that will ever be in Smash. That said, I think there are five to watch out for.
Ring Fit Adventure
Astral Chain
Advance Wars
Golden Sun
Rhythm Heaven
Ring Fit Adventure and Astral Chain have just recently come out and have been successes. I'm just waiting for Nintendo to commit to either IP by making a sequel or including them in Smash like ARMS. Advance Wars is an older IP with a history of success, but also a history of failure. This new remake may be the shot in the arm the franchise needs and if it stays around, I'd argue its only a matter of time until its included. Golden Sun doesn't have a foreseeable future, but there is significant demand for the IP to make a comeback. If any other IP makes an Advance Wars style comeback, I think it would be Golden Sun. And finally, Rhythm Heaven was already set to be in Smash at one point. It just got cut for some reason. If the franchise has a successful new entry, then I feel it can definitely get a second look and get included.