This is a good and bad idea imo.
Would be great to have a "view active invites" page and see who has invited you to their guild. But would also be the biggest waste of time and biggest annoyance for certain coveted members to be beasted with auto pm's saying they are wanted by another guild.
To be honest, if a guild wants you that much, you will already be speaking to the user actively enough to ensure a verbal invite has been granted, and then you get choice on where you go. Invite feature would be abused imo!