Better interoperability with Outlook has got to be good for any product targetting SMEs.
I like the look of this but if its free for less than 15 users, I assume that means its not free if you've more than 15 users. So that would rule it out from being freely distributed with SME & so it would have to be a contrib - or optional in some way, which may confuse matters.
An alternative approach maybe to use an IMAP server with ACL support like Cyrus. This should be no problem for licencing & those people that want Outlook folder sharing can use connector products from Toltec or Bynari or whoever - OK that means a cost even for licence 1, but may be a simpler approach (Until there a full GPL alternative).
I've had Cyrus working on 5.6 & now 0n 6.0 (there's a howto on my website
www.westcountrybusiness.com, although not yet updated for sme6). On SME 6, I also got it running with WebSieve - a web interface to allow users to edit Mail Filtering Rules - it can also work with Procmail (with a bit of 'tweaking')
I wouldn't like to claim its been tested robustly enough to simply become part of the disto, but if working with Outlook becomes a popular issue, & Cyrus is considered an option, then I'm happy to pass on any work done to date.