I like the idea but...
-> Make another option then just login by facebook, maybe a otland account or a special mapping account, where you can link your account with ot community websites. Or with a small profile information on hover? -> Able to use your own items.otb / items.xml / dat and spr, you can upload it and will be temporary saved based on your cookie settings?
-> able to choose which client your working, based on that the dat/spr/otb will be set for you.
-> Control settings? For example G = Minimap on/off Scroll = Zoom in/out or just scroll?
-> Maybe something like save mode? For examle browser crashes or something happens suddenly that the latest back-up will be mailed to you?