Replacing the rfc2388 system by something that is better has been on the "should be done" list for a very long time. Are you volunteering to either repair it or come up with something that is better?
I also think that a replacement is needed (I have another patch lying around that is needed for missing final MIME boundaries).
Time is a problem, though. I'm going to put it up on LispNYC's list of SoC projects I'm willing to mentor. Should no one turn up then I'm likely going to work on it myself in a couple of months.
Leslie