MK11's valuable gear pieces should keep being reused, in MK from now on (in different ways). Can't of done so many in the custom system for nothing, they need longevity. Customization mode can still be sacrificed for simpler costume selection options to choose from rather than creating a look. Another MK would still need to bring something new to the table though.

Onaga returns

I agree, NRS should look at some of the Mugen content. I just saw some video of Jataaka. And she her moves and fatality really separated her from just being a clone. She actually looked really fun to play too! But yeah, I think looking at those games and some ideas or concepts from some of the minor characters could help some of them become a reality.

I would like other characters to be playable. I'm for a decent chunk of the MK Trilogy characters to come back, but it would be great to see some 3D characters and some minor characters get a chance in the modern games. And I know some people love them but fewer guest characters.

Also, as Masr said, the customization needs longevity and should continue to be used. And throw in previous used looks for those characters as well. I enjoy earning a new skin or piece of gear. It really makes it feel like it's your unique version of that character.

Story: The return of Onaga.

Characters: The klassic roster, with some 3D and HD Era characters, and two or three new ones (playable). Design change (I personally don't like the clothes design in MK11 in most characters)

Gameplay: More like MK9 than MK11. Fast-paced, four variations. Stage fatalities, Tag-team (tag fatalities maybe?)

Also I would like that NRS make one of two things: Animated endings for the arcade mode, or three endings for each character, one Evil, one Good, and the other Neutral or something else, wich depends on how do you play: if you kill your allies, you get the Evil ending, if you show mercy with the majority you get the Good, something like that. And I say one of two because I know it would be pretty much for the company to do both. Also I got bored of the same low animated endings in MK11, they were cool until MKX.

Something I would like to see return are Animalities, but It would be pretty how to explain that the characters could transform into animals, and I know they are infamous among MK fans. Maybe if the characters have an amulet that let them morph.

A new Kreate fighter would be interesting, but tricky to make it balanced. Also how the hell would be the arcade endings?

DLC: two with side stories, or a sequel like MK11 aftermatch. Two guest characters at max.

I am not saying ALL of this should be in the next installment, just that they could be considered.