can back end keep track of *all* group info?

[Paul Grayson <pgrayson+ding@ks.uiuc.edu>]

I'm writing a simple server that will allow me to access a huge
maildir (10,000+ messages).  I split the messages virtually - my
server applies splitting rules *while* you browse through your mail. 

My server keeps track of marks, and could report the number of
unread/flagged messages in each group for display in the *Group*
buffer.  I don't want my server to count the total number of messages
in a group - that will take too long - and I want to avoid the nnimap
problem of always having the unread/flagged count out of sync with the
server.

I love everything Gnus does, and really want to use it as a front end
to this server - is there any way to write it a back end?  I've
experimented a little, and it seems that Gnus generally requests much
more information than it uses, but checks too rarely (with, for
example, nnchoke-request-update-info) to keep the information
up-to-date.  Is there any way to trick Gnus into letting the server
keep track of everything, or would it mean rewriting a significant
part of the front end?  Are there any plans for allowing this in the
future?

If I don't want to rewrite parts of Gnus, is it possible to write my
own group-browsing mode and connect it to the Gnus summary mode?

If you think this is not worth the work, is there any other email
back end that lets you instantly re-split tens of thousands of
messages?

Thanks!
-Paul