Sinister dampened down Gambit's New Sun like powers when he was 18 years old. It was clearly stated in the first Gambit series by Fabian where the New Sun series was written. Gambit was to marry right after his eighteenth birthday and then of course had to leave the Guild because of the killing of his brother-in-law at the wedding and subsequently ending the marriage on the spot. The Gambit series states that in his travels right after that is when his powers start growing out of control, this is when he meets Scalphunter as Grey Crow and doesn't know that the man already knows Sinister and it as assumed when his out of control powers have something to do with that theater in Seattle. Sinister operates on Gambit to tamp down his powers in return for Gambit working for him on some specificed number of tasks with the last one being the marauders.
Gambit is well in his 20s by the time he meets up with the X-Men (there is a statement somewhere about it being nearly six years since he had to leave the Thieves so Gambit was about 24 when he first meet Storm.
Given that the Massacre was a few years back Marvel time prior to Gambit joining, Gambit worked on and off for Sinister as required from about 18 to 21/22 years old until he completely repayed the debt with the last task and got the capsule with the part of himself that was removed to damp down his powers. I would suspect that Sinister just shown up every now and then in Gambit's life to ask him to steal something for him for those few years since we know Gambit was out and about all during those years traveling around via other stories of Gambit's past.
Then after joining the X-Men, after Antartica, and during the New Sun time in his book, Gambit went back in time to save his father and had the Sinister of the past replace the part of him that allowed him to tap into his full power again. Gambit seemed to be getting a handle on his control much better than he did as a teen and could time travel, as well as trvel between dimensions and just look at someone and affect their molecular structure through kinetics including blowing anything or anyone up. In his final battle with New Sun they both expended alot of energy and Gambit says he used up his extra powers. Personally I think it makes more sense Gambit has a mental block about them since he never wanted them in the first place knowing how dangerous they were and New Sun confirming how deadly there are since he destroyed a whole world.
So I would think the potential is still there but it's highly unlikely Gambit will ever tap it again unless something terrible happens).
