One Tamriel arrived with yesterday's update 12. This patch has a whole host of tweaks and fixes (and full notes are here) but the really big change is that now you can play any part of the game regardless of your level or your chosen alliance, and with any other player. The only remaining restriction is on the DLCs which require you to specifically purchase access unless you have an ESO plus subscription.
All areas of the game will have dynamic levelling as well since previously an area which was low for anyone in the Pact would have been a high-level, Cadwell's Gold area for anyone in the Covenant.
Even Craglorn has been reworked so the questing is more like the other areas and is not only for groups.
As a trading guild we've have always had a very multi-alliance focus anyway and our members are a wide mix of home alliances and levels. This has sometimes hindered members attempts at more social interaction. Many times there's been a call in guild chat for someone to join a group for some activity and some members have been interested only to realise they are a different alliance to the person making the request. Now that will not matter.
So, we're free at last, and have new opportunites for more interaction within the guild :) And don't forget that joining in any events created by guild members can earn you a badge - see previous news article for full details of the guild badge system.