i believe such a solution is not necessary for a few reasons.
first - quality of modding and bns. while it does indeed appear that there are "too many bns" (a sentiment which i don't exactly disagree with) the solution is not to nuke the entire system but rather to use the existing mechanisms more. probation at the moment is completely useless. i'll quote a certain someone here: "as long as you don't literally rape a girl on probation you'll pass." QATs can regulate the "quality" of bns by using probation and removal of BNs who consistently break rules, nominate over unrankable issues, nominate consistently low quality maps, only nominate maps of mappers in their friend group, etc. all these things can already be prevented by the QAT, they just need to start doing it more.
second - an arbitrary threshold is not a good way to judge someone's ability to contribute meaningfully. look at various bns who were active with, say, low amount of ranked maps. naxess, wishkey, dsco, as well as various others in times past. similarly, low kudosu count, or high kudosu count, isn't a good way to judge either. there are plenty of very high skilled modders who do not mod regularly or post mods, preferring to help people in irc or whatever. there are also a lot of not-good modders who have extraordinarily high levels of kudosu - not gonna name names for obvious reasons.
third - there are already a lot of unspoken "objective" criteria as well as the actual objective ranking criteria. you won't see many maps that do not even attempt to follow the song, despite there being no objective rule against it. i assure you that all these awful maps that you see being promoted are being promoted by BNs that have different values than you - not lower standards, not circlejerk, not malicious intent.
fourth - mapping is not more or less diverse compared to previous years. i promise you that these similar types of maps that you crusaded against were being promoted in 2012, 2013, whatever, as they are now. similarly, the type of maps that you promoted and see as quality content have also been promoted and are consistently promoted to this day. the difference is in the level of personal involvement with maps outside your "bubble" - you started looking at many more maps, i assume, which is why you started noticing these terrible maps more recently. i realize this sounds extraordinarily presumptuous, and it may indeed be completely wrong with regards to your experience. but i firmly believe that mapping has not evolved or devolved in quite a long time. the same ideas that are prevalent now were prevalent since a really long time ago. the only difference, really, is the inordinate amount of terrible 1-2 pp maps, but that has nothing to do with this proposal.
in sum: i don't think sweeping changes are necessary as the situation is not particularly unique. the tools to deal with "low quality" bns are already in place, simply unutilized as far as i can tell.