I read these proposals quite carefully, but in the end, as it involves my validator I am afraid that I am not totally objective, and that is why I usually avoid to comment in the BLS limit topics. But here it is my opinion.
If there is a real danger that one validator could take over one shard, that risk must be minimized or removed. But we are talking about a group of validators joining together to take down one shard. In which interest they would do that? Being a validator is a responsible and, in the end, a profitable business. Having the power of doing that would mean that you have such stake/delegations that the last thing i would like to do is to risk my position, or invest a large amount of money to perform wrongly (and probably risking it). I am a naive person and I am sure there could be malicious intentions behind taking down one shard in which the attackers could benefit of course.
So i vouch for safety, but I dont think it is a real risk that a group of different validators come together to act against harmony, damaging themselves in the process.
And second, I don’t like restrictions unless-totally-neccesary. Do you want to spread the nominations? Then I am sure there are better ways than forcing people/companies to split their stakes against their will or imposing hard limits just for the shake of descentralization. I know the way harmony is designed, but there are other protocols that they incentivize staking to smaller validators, and punish to delegate to oversaturate validators. That is for me where you get the real descentralizacion. Do you want to stake with a validator because you feel safer even if you get 2% less rewards? That’s totally fine, it is up to you. A little like substrate projects.
In the end, currently lage validators are the most interested in having the highest uptime and the best performance. In the past I invested heavily in my own two bare metal servers, one in Spain and one in Amsterdam, two countries where I live/work/move between. Some months ago I had to move to VPS because the traffic increase was too much for one of my ISPs at one location and I didnt reach the uptime I wanted, so I moved to VPS temporaly. Again, two server, different providers, heavily oversized.
I just want to stress that I dont believe that large validators would join to overtake one shard. But I do believe that one large validator could be offline for some hours/day not on purpose, and this is the point that we have to avoid.
About this proposal, I agree with the idea that set up a limit having a X% of the total shard, but I dont think 6.4% is a lot. I remember that we were looking for shard leaders, and the requirement was to have at least an amount of keys in the required shard. Are these two ideas compatible with the 6.4% limit? To lose consensus with the 6.4% limit at least 6 large validators have to be disconnected at the same time, which I dont see it realistic.
PS: honestly this is not affecting me at all, because I have exactly 14 slots and I could go for lower if I wanted. This is just my opinion about all the limits that we are reading about lately.