Xtracycle-style Sierra?

I don't know if it's possible to do this with an actual Xtracycle due to it's frame construction, but I am pondering an Xtracycle-like addon (that will do this) to that Schwinn Sierra I fixed up recently, perhaps with a motor assist, perhaps not.

Specifically so that I am not dealing with a longer shiftline and the problems reported with it where shifting can be finicky in one gear or another, I intend to put a regular rear hub with the derailer still on the Schwinn's dropouts, so the original chainline stays as it is, as does the shifter cable. Then there will be a separate sprocket from that hub to the rear wheel, which will be re-laced to a no-dish single-speed wheel to make it stronger for cargo use. (actually I will probably just take a front wheel with a sprocket bolted to it, for simplicity of testing out the idea).

I will probably build the addon frame around an existing rear triangle off of some other bike. I am tempted to use the one off the white Huffy, simply because it is called a "Nevada", which would make this bike a "Sierra-Nevada". ;-)

But that is a silly reason to pick a frame, so I will more likely start with one of the old chromoly tenspeeds I have, whose frames are way too tall for me to use for myself normally. I'd remove the entire rear triangle from the donor frame, but not including it's BB. I would cut down the seatpost from the bottom end, leaving that extra on the BB itself. Then reweld the seatpost and chainstays to a new crosstube from something else. This would all be welded to a subframe that can then bolt to the Schwinn Sierra's rear frame and keep the whole rear end stiff. It would mount in such a way as to leave a clear chain path between the Sierra's rear dropouts and the new rear wheel position, and would be able to slide back and forth for chain tension adjustment and lock in place to hold it once set.

I would like to make some bottom/side rails that let me rest cargo on them (like some Xtracycles do) that are removable, so I do not have to carry them for typical rides, but instead only when I will carry more than normal stuff with me.

Then a top deck to cover the entire space from over the rear wheel to the back of the seat.

I am also considering a more recumbent seat design that would fit down into the gap that could exist between the tire of the new rear triangle and the Sierra's seatpost/seatstays. Then I would move the steering handlebars back to fit in a bushing in the seatpost, and a linkage for remote steering to a stub-bar up in the original stem. This is a very similar arrangement to Justin's (of http://ebike.ca) cross-Canada bike, and inspired by it.

The problem with such a design is that it reduces the cargo I could carry on it, so I would (as Justin did) likely leave the option of pulling off the remote steering and inserting the original seat and post, and riding it just like that. The 'bent seat would stay, as it would make a nice carrier for some cargo. Well, unless the cargo was too large and needed to fit across the full length of the area behind the seatpost.

Just some thoughts for another possible cargo bike, most likely quite short range in nature.