Stylesheets are one of the easiest ways to produce problems
with different browsers. Taking a step like the one you
suggest would rapidly result in a site that was only
navigatible in recent versions of IE.
That would be completely unacceptable to me since at home
I use Netscape on Linux. If vroom took a step like you
suggest and problems cropped up I would publically announce
my reasons for leaving and if that didn't solve it I would.
Certainly the stylesheets at a few home nodes has led
to my avoiding certain people's home nodes. But the fact
that the problem is localized has made it (almost)
acceptable so far.
So I really, really don't want vroom to allow people to
use their own stylesheets everywhere.