I've looked at building a 6.5-.375 but came to the conclusion that the best balance for my purposes is achieved with a 6.5-06 Ackley. More bang for the buck, less recoil, plenty good to 800 yards, and brass is easy to fabricate.
The -.375 version, if based on the .300 RCM doesn't offer much as it has less case capacity than the .264 Wby. The full-length .375 case would provide 105g powder capacity or so, too much for my purposes. I considered forming cases with the shoulder set back .2-.3" but just couldn't see the advantage since I'd have buy custom reamers and dies and case forming would be a pain.
The 6.5mm-06AI should provide about 72g capacity, the same as the .300RCM and about 4g more than the 6.5mm Rem Mag.