Yeah, plenty of portable games could use remasters. There are two Kingdom Hearts games on DS, 358/2 Days and re:coded (lmao those are silly titles ain't they), but they were only included in the HD collections as remastered cutscenes. Freedom Wars on PS Vita really ought to be brought to TVs and PCs. That's one of those games where as I play, I'm craving to switch to mouse and keyboard.
Star Wars Battlefront: Renegade Squadron & Elite Squadron, both on PSP, in some ways improve on the previous Battlefronts. They're both fully feature-rich sequels to BF1 & 2, with new additions such as customization, and a real storyline in their campaigns, especially for Elite Squadron, which chronicles a Jedi's clone from the Clone Wars to beyond the Galactic Civil War. If you've seen the leaked gameplay and cutscenes for Battlefront III, you've already had a taste of Elite Squadron, which is what BF3 became. Rahm Kota, from The Force Unleashed, also makes an appearance. These two really ought to be remastered in HD.
Borderlands 2 for PS Vita should be remastered cuz it'd be funny