Please add this feature. This is sometimes very necessary.

Use their UUID instead of their username is they haven't logged in before. Luckperms doesn't know the username exists without them logging in first, but the UUID gets around that.

I have a crack server :(

Quick googling reveals that you can generate the offline uuid if you have the playername.

You can enable it in the config already.
https://github.com/lucko/LuckPerms/wiki/Configuration#use-server-uuid-cache