I don't think we need to do anything special for exec, as the exec(s, locals, globals) syntax is already (still :-) supported in 2.x with identical semantics as in 3.0.

except E as V *syntax* can go in without a future stmt; and (only when that syntax is used) it should also enforce the new semantics (V must be a simple name and is deleted at the end of the except clause).

I think Anthony's patch is a great idea, but I'll refrain from reviewing it.  I'd say "just do it". :-)