Hey everyone! It's time for a new "Gold Line" map.
https://drive.google.com/open?id=1GHh_W1GpQ5Ur5HrIwfkCt2BF7UAo0k2_&usp=sharing
Our maps for Seaport BRT generally use the Surface Artery and continue to Charlestown, but there's really no reason to do that. The Surface Artery (as others have noted) is indirect and really misses a lot of key trip generators, with the exception of the Aquarium. On the Charlestown side, there's just not much over there yet, again with the exception of some tourist hubs.
On the other hand, there's an enormous desire line from Kendall, to North Station, to South Station, to the Seaport. I drew that line, with a terminus at the Design Center to accommodate the transit-poor corporate headquarters currently going in there (and more of those in MP's office development in the next decade).
This routing - to be supported with all the best BRT accoutrements like all-door boarding, island bus stops, off-board payment, etc - could be largely paid for by the cities of Boston and Cambridge. Vehicles could be sponsored by companies - buy a bus = wrap it in your colors. If they're going to buy shuttles anyway and join together on shared shuttle services, why not just ask for their help with this?
The MBTA would need to be engaged for a maintenance facility. I drew it taking over the Red Line Test Track layover yard when that procurement is done, but it could also be built into the bowels of a BCEC addition. The layover yard on the Kendall end could simply take a corner of the new Volpe's parking lot.
I didn't draw this as continuing on to Allston on the GJ, but it could.