This is not an answer that will work for growing Lemmy. Most people do not want to buy a server and domain name to use Lemmy, and then they gotta learn how to use Linux and docker and figure out how to get it all working? Most people don’t even know what Linux or SSH is. And then they need to read a huge list of instances to see which ones they want to block? And they gotta worry about keeping it up to date, and security issues, and watch the disk space usage. They would rather just stay on Reddit instead.
Also your solution still doesn’t address blocking/hiding posts but not comments, or hiding posts in the feed but still showing them in searches or in the specific community.