In this year's R2AK, Team “Fix Oder Nix” raced in a “stretched” (24'6" LOA, rather than 19') Sailing RowCruiser. Their extension included a second smaller cabin for an additional crew member in the aft end of the boat. Links for the curious: blog, Facebook, R2AK profile, Die Yacht article, Soundings article.
I'm about to get started on a SRC build, and while I don't have a whole lot of interest in a second cabin, I can't help but feel intrigued by the idea of a slightly stretched version of the SRC. Adding just one or two more feet in length at widest part of the hull, and then moving the aft storage compartment bulkhead forward a bit, you might be able to fit a full-sized bicycle with 700c wheels. Plus, the waterline length would be increased (good?), and the rower's position would be brought a little bit closer to center (also good?). The only drawback I can think of is the additional weight, which can't be much.
I'm very curious about other people's thoughts on this modification.