While I'm not especially a huge fan of the Temporal Cold War, I can see a lot of potential in the unseen Chef being trained up for a mission to stand-in for Kirk.
A lot like the TCW itself really. Promising start, a couple of interesting episodes connected to it but disappointing and hasty conclusion. Too many questions left unresolved, like Future Guy - despite comments since that they planned to make him a Romulan. It frustrates on that level, on rewatch, things that feel important but we'll never see resolved.
But clearly having watched the Captains documentary, and Bill & Scott alongside the others touring conventions around the globe, they do get on and it's a dynamic I'd like to have seen happen in Enterprise. Particularly if he'd have played Chef with the same tragic/comic angle he did with Denny Crane. Another part like Quantum Leap's Scott/Dean double act.
Probably would've been played for laughs to start with, senior/junior actor role reversal and then something goes horribly wrong, leaving Chef to actually be James T. Kirk. Maybe even remain in the future, with absolutely nobody twigging a switch has happened. Possibly a way to fix Shatner's dissatisfaction with Kirk getting killed off in Generations... without undoing what had happened.