Is Beyond Good & Evil 2 actually happening? If not, then that's my #1 pick. Excellent game that ends on a cliffhanger.

Other than that, I always wanted a follow-up to Jade Empire. I agree with @Vodacixi about Pokkén Tournament. I think Kameo: Elements of Power deserved a second chance.

I'd love to see Diddy Kong Racing 2. Imagine a true adventure mode in something as big and dynamic as Mario Kart World. It would probably be the best game ever made :P

PS All Stars of course.

Snipperclips and Arms. I really loved the latter game but it doesn’t seem Nintendo agrees. Last mention of the game was back in 2020 with no NS2 Edition in sight being that it has already been patched.

But if Mario+Rabbids and 1-2 Switch could get a sequel, then there’s still hope!

Ryse: Son of Rome

Sunset Overdrive

Quantum Break

Dante's Inferno

..... just to name a few.

Mischief Makers was a fantastic N64 game that kind of flew under the radar that i wished had become a franchise.

Vanillaware has the bad habit of not doing sequels, and most - if not all - of their games are pretty solid. In recent years Unicorn Overlord hooked me hard and its a shame to know they probably never will make a sequel for it.

Bloodborne obviously. 

N64 - Blast Corps & Pilotwings

Both unique experiences. Blast Corps probably wouldn't work as a full fledged modern game anymore but could make a good mobile or small downloadable game. (preferably the latter to avoid touch-screen controls)

Pilotwings turns out I am wrong it wasn't standalone, didn't know there was an original on SNES and apparently there was a 3DS one.

As far as I'm concerned 3DS one never happened. It's not Pilot Wings. It's just a Wii series game with the Pilot Wings name. I have waited 30 years for a proper sequel to the N64 game. 

Sunset Overdrive
Hi-Fi Rush (although I guess that’s TBD)
Bulletstorm
Grim Fandango

Black
Vanquish
Blast Corps
World Driver Championship
Quantum Break (RIP Lance)
Jade Empire
Crimson Skies

If we count sequels that were amazing and never got a sequel, Titanfall 2

Tokyo Morage Sessions
Metal Gear Rising
Vanquish
Kid Icarus
Conker's Bad Fur Day
Legend of Dragoon