MIME parameter lists?

I guess my feeling is that

1.  It is indeed too late to make this change.

2.  You can get the effect you desire anyway, so long as you use a
quoted string, e.g. while you can't say:

Content-type: text/plain, x-something=one,two

you can indeed say

Content-type: text/plain, x-something="one,two"

which is almost as good....