beamer heavily relies on \special and this does not work in RTL mode in XeTeX and so fixing beamer for RTL in XeTeX does not make any sense. If the issue of \special in RTL mode is fixed, then beamer can be easily modified for RTL typesetting otherwise you can not expect much.
I think the original beamer package should provide bidi support so I recommend you contact beamer maintainers and ask them for bidi support in beamer. but if you want contribute code to fix beamer in bidi, you are more than welcome to do so. -- Best wishes, Vafa Khalighi
-------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
