Found a 650b 140mm Yari that states it is torque cap compatible (115mm and 100mm).

I assume this means it doesn’t ship with the caps, and that said caps are limited to certain hubs, eg Hope’s version?

Yep
The caps are part of the hub not the fork.
The fork will however still work with standard end caps.
Just makes it a tad more fiddley to fit the wheel.
I’ve got a boost fork running a none boost hub without the torque caps and an additional 10mm spacer just to make it even more fiddley. 🙂

I’ve pondered buying the Hope ones for Pro2 hubs on Rebas but haven’t been able to justify the cost vs the minor inconvenience

I am weak and got fed up of the fiddle so got a pair of caps for my DT hubs. I have not however, been able to discern a noticeable decrease in anti-torque, torsional un-stiffness or steering inaccuracy.

Ok, sounds a bit of a bind unless everything marries up correctly. I would’ve thought disc alignment one of the bigger challenges?

Think I’ll pay the extra and go non-Boost. Cheers anyway