Mariko is a cert.
I will be pissed off if we don't get the Silver Samurai in the Japan movie, we need a great fight between those two, his mutant energy channeled through his sword can cut through Logan's adamantium bones(according to issue 2 vol1 of Wolverine), so he has to be in there, an opponent who actually poses a serious mortal threat to Logan.
Sunfire would be good too, he was always good value as a loudmouthed arrogant type.
I would also like to see Gambit return as I liked their buddy vibe on the plane in xmo:w. But, I think I would prefer him to accidently run into Logan in a 3rd movie set in Madripoor. That seems like the kind of place a gambler and thief like Gambit would end up, instead of just having him randomly show up in Japan.
If he doesn't show up in a Wolverine solo flick, I'd like to see him in one of the First Class movies. Ideally both, have him in X-Men, have him leave the school, and then show up in Wolverine 3, so they can all be linked up in a cool way without Logan cameoing in X-men, which would be a mistake.
I thought the kid was good as Gambit, they should definitely use him for another X-film.
I would also like to see Rough-house and Bloodscream, ideally in Madripoor, but Japan would be fine too.
It's a pity they wasted Lady Deathstrike as nothing more than a sfx in X2, she would have been good for a Wolverine solo.