Look, I can do a "show interface" on any interface and see what speed
it's running at and if it's dropping packets. If BGP hears a route
on an interface that isn't dropping packets shouldn't _that_ route
be considered "best" all other things being equal (hop counts and
all)? You can't tell me the router doesn't know this information
because _I_ get the information from the router itself!!I understand about route instabilities, etc. All I'm talking about
here is a better "tie breaker" than ordinate numbers of IP addresses.
The router really can't see how fast an interface *can* go unless it's
maxed out. That's not really useful information in a route-selection
decision.
It's possible that the packet loss might weight a better path but you
would have to be careful about reweighting 20k paths every few minutes...
Especially if you pass those decisions on to other routers 
Avi