I hate to have to revive this long thread but is there anything going on ranking-wise? I think this is really needed to preserve the playerbase.
Even if it is only a win/loss ranking system rather than the fancy algorithm learning. I've read through this thread a couple of times and I don't really see a viable argument against making changes.
Also I have something to contribute

. Both of these ranking systems has the flaw of not working from the start (not even remotely!), as there is not enough data.
http://www.quakelive.com has come up with a good solution for this! By checking skill through a tutorial that asks you to do various tasks. Such as rocketjumping, jumping various lengths and some other stuff, to increase in temporary levels. Sort of like a trick map actually but pretty much easier than conventional ones. The last part is a match against an easy bot to do the last tweaking. It gradually increases its skill if it gets killed a lot in the match and it's all over after 10/20 kills if I remember correctly. I don't know if an AI in spring could do this but it shouldn't be too hard to like make something like a chicken map to test a player... This could somehow be implemented in Spring when you first install it. It could be like "kill these two aks with your two rockos" in the beginning or something like that. Sort of like a campaign. This is actually a
very fun way of determining skill and it greatly increases the overall experience. A huge opportunity for spring! In quakelive this data is also (fast) replaced with factual match data results to replace the tutorial. In quakelive I'm pretty sure only highscore result is drawn when calculating rank.
tldr: check out
http://www.quakelive.com and awe.