Some of my colleagues swear by logseq, but I personally haven't used it. If the upcoming sync feature would be available to self-host, I might consider switching to it, as it would combine multiple services that we are currently using.
It seems to be file based, so wouldn't it be able to use other self-hosted sync-tools like the next cloud client (given you're hosting your own instance)?
Depends ok the cloud solution you use, but it definitely could be an issue. Probably not because of locking, but because the files probably aren't locked with the clientson there could be issues while merging the changes.