I'd like to see Jean date outside of the X-Men. Namor would have been a fun choice but I wouldn't want her to tread on Emma's leftovers. Rogue already burned Human Torch.
It should definitely be an Avenger and I think Bruce Banner is long overdue for a new romantic interest. Jean offers a unique bond with her ability to reach Bruce even when he's in Hulk mode. Beauty and the Beast-esque.
She needs someone with an edge so a reformed villain or antihero would be preferable, too.