I think a good way to bring Sunspot back into the fold is to highlight that he is a successful businessman that has credible ties to other superhero groups.He could also be the financial backer to the X-men. This gives him the flexibility to have a prominent world in the X-men without him having to unseat any longstanding X-leaders to play a pivotal role. it provides the opportunity for Sunspot to have a important role in the X-men operations. sunspot could give intel on anti-mutant activities and select certain X-men to deal with it. Similar to the Domino side story in a annual they appeared in.