Hi list,
After doing some studying on my own I can now better rephrase one of my key 
questions about citing e-mail and news posts.
Briefly put:

How do I make emacs: a) infer the fil prefix from a line, b) make paragraphs 
a set of contiguous lines with the same fill prefix repeat count, c) protect 
the fill prefix from editing?

I really like refill mode legally blind, it let's me concentrate on the text 
rather than caring about line breaks. Snipping quoted text then becomes a 
matter of setting the appropriate fill prefix and editing the paragraph in 
question. I can also just regexp search for the next level n quote ( 
^\(>\s-?\)\{n\} ) and kill from my search start position to the destination 
quite easily. Pretty nice.

The only things Emacs does not do is infer the fill prefix directly from 
line beginning, set paragraphs to be equal to a particular quoting level 
(fill prefix n times), and make sure that I don't snip the fill prefix (>) 
when killing sentences, for instance. So the question is, can it do these 
three?

I have looked at various modes like post, filladapt and so on but none of 
these are quite what I'm looking for. The best solution I can think of right 
now is to simply use single space indentation for e-mail quoting levels and 
convert between the equivalent number of spaces and > signs via a global 
regexp replace both before, and after writing. Maybe that will due the trick 
once I get used to it.

it still doesn't protect killing and movement in textual units like 
sentences and beginnings of a line, I guess, and neither does it handle code 
snippets with indentation.

If Emacs can manage the > signs on its own, there's absolutely no need for 
me to cursor to them let alone edit them, much the same attitude as levels 
of indent in code in a smart IDE.

Any help appreciated.

-- 
With kind regards Veli-Pekka Tätilä
Accessibility, Apps and Coding plus Synths and Music:
http://vtatila.kapsi.fi