You have made me reconsider the Co-Motion which was near the top of my list.
Bicycle Quarterly tested the "Nor'Wester Co-Pilot" and found that it weighed 28.8 pounds without lights and bags, that the heavy oversize tubing was overly stiff, and that it was difficult to ride in a straight line when the rider was tired. I have no personal experience with the bike, but this is a less-than-glowing review from what I consider a reliable source.
I agree about the fenders being a PITA and will be taking them on and off as the seasons change.
This is the one area where plastic fenders may outperform metal. Properly installed aluminum or stainless fenders are semi-permanent, although I'll bet Bmike will disagree!
Regarding gearing, the range I am baselining to (48/36/26 and 11/32) is about the same as my Roubaix on the high end and is about 0.6 times on the low end. I originally planned a 44/32/24 but really feel this is too low (might regret this some day). I live in the N. California coastal mountains and there are lots of 5 mile runs at -1 to -2% (going with the prevailing wind) where one can easily maintain 30 mph
so I think the gearing is not too high but high would be first to go if I have to compromise.
The top gear listed is good for 38.5 MPH at a comfortable 110 RPM. The bottom gear will make for a stately 3.5 MPH at 60 RPM. The top gear is good for field sprinting with a 1/2/pro field, and the small for loaded touring up the inside of a well. The downside is massive jumps between cogs. That would drive me out of my mind, but you may be different. I need a gear that will allow me to go maybe 6 MPH up the worst walls, and I stop pedaling above 30 MPH. So for me, I can use a 46x14 as a top gear and a 30x25 at the bottom, which gives me very close steps between cogs -- one tooth increments most of the way, with a nine speed cassette and a 46x30 double. And of course, anyone who wants something different from what I want is a fool and probably a Nazi.
I really hope the S&S couplers live up to my expectations since I guess that is the one thing I am committed to. Nobody around here seems to have them so no first-hand experience base to go on. The reservations expressed here are the first I have heard. Does anyone else know whether these are flawed?
I used to coach a guy who ran an LBS specializing in tandems. He had a lot of bikes come through with couplers, and a lot of them gave trouble, which is how I came by my opinion on the subject. It was reinforced by, again, Bicycle Quarterly, which wrote about a test bike that rattled, flexed, and shifted poorly -- all problems which were eventually traced to a self-disengaging downtube coupler. And now matter how much it was tightened, it would work itself loose again.
A frame that disassembles itself seems like sort of a bad thing to me, but YMMV.
HTH!