mastercomsUpdate on the fixed weapon spreads: it resulted in worse play than normal, since the fixed seed for the weapon spread could be terrible to aim with, while a randomized seed plays better, since there's even chances of god spread and bad spread, so you aren't stuck with any one spread. It's pretty hard to find a seed for a pattern that's truly "average", so I think randomization is a better way of averaging this out than a fixed one.
Also about multi-threading, I don't think Source really needs much more multi-threading than it already has
Could a fixed, 100% accurate spray be created from, say, suppressing the getbulletspread function or returning a perfectly accurate vector when a weapon fires?
Don't know anything about the TF2 source or C++ but those hyperlinks I provided seem like the heart of bullet spread for auto weapons.