Not going to argue the merits of 6.5WSM vs. 6.5SAUM.
however, don't let "lack of dies" scare you away from the wsm. Just use 270WSM dies. Buy the VLD type .277" seating stem and the size appropriate bushing you need for 6.5mm.
The dies everyone are using for 6.5SAUM are just 7 SAUM dies, with a 7mm VLD stem.
Yes, the bullet fits in the seater like a hotdog down a hallway, but it works fine. Actually, the .264" bullet will be a closer fit in the .277" 270 die than it is in the .284" 7mm die.
As for chambering reamer and gun smithing - it's no different than any other cartridge. You'll order the reamer from PTG, JGS, Manson or Hendrickson, then give your action, reamer and barrel to the gunsmith of your choice.
I guess I will make one point about the 6.5saum: Bunch of gunsmiths already have that reamer in hand.