Is the "insularity" of the 10K+ community really a concern? The same can be argued for 5K, 8K, and 9K where only a small handful of people rank those keymodes yet there are no complaints about those communities being insular and closed off. It's better that there is a community around higher keymodes to begin with as it indicates that there are people interested. I imagine that if this goes through, you'll see more people pushing higher keymodes now that there is incentive to do so (getting the map ranked instead of graveyarded or loved which gets less interaction than ranked).
To answer your first few questions regarding how many people have ranked 10K+, K0nomi's post here gives a good handful of 10K+ maps to start with community/forums/posts/9181718. I don't understand why it's such a concern if they belong to the 10K discord server or not, it's just a platform to gather like-minded people about upper keymodes to help each other out and push 10K+ maps.
Regarding BN judgement, BNs have never been required to know more than just the keymodes they nominate, i.e. there are many BNs who are 4K only and don't nominate other keymodes, so it'd likely follow that BNs don't need to be capable of nominating 10K+ maps if they decide they don't want to, assuming they're proficient in another keymode of their choice. As for checks to whether the BN is capable of judging or not, I'd imagine it's the same as it is now where their judgement is evident in the quality of the maps they push - regardless, this is something that is up to the judgement of the NAT come evaluation time for BNs as to whether they're capable or not.
To answer your first few questions regarding how many people have ranked 10K+, K0nomi's post here gives a good handful of 10K+ maps to start with community/forums/posts/9181718. I don't understand why it's such a concern if they belong to the 10K discord server or not, it's just a platform to gather like-minded people about upper keymodes to help each other out and push 10K+ maps.
Regarding BN judgement, BNs have never been required to know more than just the keymodes they nominate, i.e. there are many BNs who are 4K only and don't nominate other keymodes, so it'd likely follow that BNs don't need to be capable of nominating 10K+ maps if they decide they don't want to, assuming they're proficient in another keymode of their choice. As for checks to whether the BN is capable of judging or not, I'd imagine it's the same as it is now where their judgement is evident in the quality of the maps they push - regardless, this is something that is up to the judgement of the NAT come evaluation time for BNs as to whether they're capable or not.