I suspect that implementors don't value "HTML 2.1 compliance" as much
as they value satisfying the market demand for tables and moving on
to other things besides file upload.
I think there is a real need for file upload, but the way to get it
deployed is for the market to let the implementors know, and not for
the standards bearers to twist arms.
Another option is for some information provider to build a killer
application that requires file upload, and for example, make the
patched version of Mosaic (and/or a HotJava applet) available. This
is a pretty high-risk operation: you're betting your application on
support that's not there yet. But at one point in time, the whole web
was in this position (vs. ftp, gopher, and the like.)
Dan