If the existing way of mixing different formats in MIME doesn't do
quite what you want that's not a reason to create a completely new
mechanism to mix formats. Why not just improve the existing mechanism?
I think you are misunderstanding the use of verbatim within text/enriched.
It is for situations such as the following:
The factorial computation can be expressed in C as a function:
int fact (int n)
if (n > 1)
return (n * fact (n - 1));
i.e. short code or text/plain snippets. Now, this could be done with a
multipart/mixed, up to a point. Note the use of <indent>. If the message
had been sent as multiple parts, there is a very good chance that (a) there
is no way to specify indenting, (b) some user agents may use a totally
different font for text/plain than for verbatim, making it hard on the
eyes, and (c) other user agents may clear the screen or do some other wierd
things that break the flow of the document - metamail is the classic example.
It really depends on the author's intention. If the author wanted to
make the code extractable, then I'm all for multiple parts, but if it
is just a short example, breaking the flow of the document is not good.
Also keep in mind that the above example could have been automatically
converted from a wordprocesor document. If so, there needs to be some
way for verbatim wordprocessor sections to be expressed in text/enriched.