ISTR my reason for not picking Athena was that the cross-domain story isn't great. You can do cross-domain stuff with CNAME hacks, except then you don't get TLS, unless Twisted suddenly does SNI or you have a cert with ten gazillion alternative CNs.

WebSockets don't have the above problem, and IIUC neither does SockJS.

I realize this is an issue for few people :)