FWIW i'm against it it does have the potential to be quite unbalancing since there is no overall GM control on it.
I did mean that this would let people break the 35bp cap on qualities, however it's fine either way. The main reason to allow it is to allow characters to buy Marital Arts* if they are allowed again. Another advantage would be for newbies who didn't realize that mentor spirits were that good and the like, or buy the Runner's Companion after a few games.
I also don't see the problems with it either. You need to disallow the Technomancer, Adept, Mystic Adept, and Magician qualities from being bought, but the rest of the problematic qualities are already banned. Sure, a magician could spend 60 karma (40% of lifetime karma) to get Type O System, but they also could have bought magic 7 for only a bit more karma and win even harder. I could see everyone spending 30 karma for Adrenaline Surge at some point, but an Edge 1 character could buy up to Edge 3 and that's enough to cover the 1-2 fights Mission adventures typically have or use the Edge out of combat instead. You could spend 48 karma for Aptitude (Skill) and to raise the skill to 7 (remember karma cost to raise a skill to 7 is doubled).
The cheesiest thing I could see if someone spending the 20 karma for SURGE II / Metagenetic Improvement X for a +1 to a high attribute. But really they likely had SURGE already so it's 40 karma for that +1. That means you only break even or break ahead at the 8+ range which highly suggested they SURGEd for that attribute already.
*- Marital Arts does have strong cheese potential. However I think it's worth the tradeoff of making life easier on the pure melee adepts of the world than for min-maxed combat monsters to spend 10-30 karma to win even harder than they were before. At the high level of opitimization, balance is already fragged.
