This is exactly how the XMPP network is made and how the social features that we are building around are designed :) You use the same XMPP account to login to different instances and everything is synchronized from the server your account is on.

You can try it on https://movim.eu/, we propose several instances across the world and you can login with the same account between them (it's still better to pick the one that are geographically closer to you to have a quicker load time).