I understand the desire, but before I can spend engineering time on this we need a repro. Nobody has been able to produce a repro and the whitelist and proper headers have been in place long before this topic was started.
As far as old browsers go we don’t even work on ie8 and will likely be dropping ie9 by the end of 2015.
I agree more checks can’t hurt but without a repro it is hard to justify spending time on this versus other features that directly benefit our users and customers.