Not sure if I just got lucky but imported the config from a PfSense 2.3x VM by changing version to 11.1 in the xml tags.
Had to reset the passwords for some ovpn users and had to re-save the config on the WAN interface before the firewall rules showed up (did pfctl -d in the cli to get back into the box) Other than that it seemed to work which saved me rebuilding the OVPN config on a load of other devices :D
Hmm on another one it imported but it disabled the console menu and none of the passwords I have work for the webUI.
Because the console menu is disabled I can't figure out how to reset the webui login either.
Edit: found the location of the script to nuke the password (already forgotten where it was)
Config imports on 2.1 work perfectly. 2.2 mostly. 2.3 barely without major hurdles like you mentioned.
This is due to the fact that a lot of config.xml layout changed in pfSense including how password hashes are stored. We can't provide reasonable forward-compatibility for this.
Cheers,
Franco