There is a very low chance this would ever happen, and as far as I know nobody is talking about it seriously. I think it might make for an interesting discussion and poll though:
Do you wish there was conditional comments for all browsers?
IE already has them, and we certainly use them. What if we could also do stuff like this?
<!--[if Fx 3.6]> <link rel="stylesheet" href="firefox-v3.6.css"> <![endif]--> <!--[if iOS]> <link rel="stylesheet" href="iphone.css"> <![endif]-->
On one hand, a totally un-scale-able slap in the face to web standards that takes us back 10 years.
On the other, a straightforward solution to fixing real world problems.
Poll is in the sidebar. RSS readers will need to jump over to vote.