I think that there is value in lowering the costs of the UR augs to make more available to everyone else outside the power gamers.
Some augs are now over 200B+ in the Aug shop. So you are right, the value of an aug is at least 100B or more in some cases to certain people. But at one point it was 2000GP and 4000GP and 8000GB, so I dont think the Aug shop prices are truly indicative of the their value to everyone. However, I have never seen an Aug go over 5B in the auction house. They may have sold for more, I just havent seen it. Allowing the CoM to upgrade Augs would likely bring the price of UR augs and the CoM down to 1B or so. Which is a level everyone can afford and allow UR items to be attainable at a UR character level.
This feature would actually cause the cost of CoM to skyrocket and aug prices would probably jump too. You’d have a balancing of the aug costs relative to the cost of a CoM but all would be higher because you’ve just dramatically increased the accessibility of such a thing. I’d be creating and upgrading stuff for days. I literally have 100s of augs I’d need or create. Moot point by now but yeah, it would go much differently than you anticipate.
Consider that Elysium gives a random UR aug after a slog of a run and is very much at the 55-60 range with true Limbo possibility. Whereas Limbo could be negated entirely in PoM just as a starting point.
Wouldn't it mean that the drop rate of UR augs is too low overall rather than the other way around?
Ultra rare augs should have a low drop rate... hence the name. If players want to operate outside these drop rates they can sink gold into the aug shop. The implementation for this shop has been explained in other posts on this thread.