They did not show the currently planned shuttle route between Bowdoin, Haymarket and State, but this is what I presume it will look like, operating clockwise:
View shuttle in a larger map
The roundtrip can probably be completed in about 10 minutes so this will likely use 2-3 buses, depending on how frequently they want to operate.
This planned route connects stations on the Blue, Orange, Green "C" and Green "E" lines but does not assist Blue/Red, Blue/"B", or Blue/"D" (except off-peak) connections. A shuttle between State and Park would assist every possible connection, however. But the T seems to have dismissed that possibility due to the one way roads and congestion around Park. I'm not sure what options they considered, but perhaps this was one of them:
View Park/State shuttle in a larger map
This loop would take about the same time as the previous option, maybe slightly less, but has the benefit of making all connections that don't involve the Silver Line. The drawbacks include the need to create a shuttle stop adjacent to the Park Street Church -- although there should be enough room -- and the possibility that a city bus cannot navigate the School Street/Water Street routing -- which I don't know answer offhand. Still, some creativity could be applied, such as using smaller buses or temporary street changes to make it work out.
View Park/Bowdoin/Haymarket/State shuttle in a larger map
If you want to avoid small streets, then here's another idea: take the original shuttle plan and add Park to it. This can be achieved by turning down Tremont Street, then back along Park Street and Bowdoin Street. Normally, such a loop would be obnoxious for people connecting from Park to State, but here we can take advantage of Bowdoin to shorten that transfer time. Riders going from Blue to Green/Red would take the shuttle from State to Park, but riders going the other way would make use of Bowdoin to shorten their trip. This obviously depends upon Bowdoin being held open full-time, as is planned. The bus stop and crosswalk in front of the Park Street Church would also still be necessary.
A few folks at the meeting called for the MBTA to investigate some kind of shuttle bus route from East Boston to the Red Line. I'm not sure if they'll consider it seriously, but let's take a look at a couple of ideas and see if they are feasible or not. Option 1:
View East Boston to Charles/MGH in a larger map
This option uses the Callahan and Sumner tunnels from Maverick to reach the West End and ultimately connect to Charles/MGH along Cambridge Street. As far as I can tell, there is enough clearance in the tunnels for buses, although they don't normally use them. Looking at Charles/MGH, the renovated station and circle are not at all friendly to buses (or people, for that matter). The road which runs underneath the station is named "Pleasure Road" (go figure) but it would require some heavy construction to place a bus stop there, as it is walled off from the station. That is unfortunate, since that road would be the ideal place for a bus stop. It seems that the most likely location for a shuttle bus stop would be along Cambridge Street west-bound as it enters the circle. There is a crosswalk to the station, and 3 lanes of traffic with plenty of room for a stop, along with a usable curb. Then the shuttle could enter the circle and turn around back east. Or, option 2:
View East Boston to South Station in a larger map
Instead of Charles/MGH, go to South Station using the Mass Pike. This essentially follows the path of the SL1. Presumably the diesel shuttle buses could not actually use the Silver Line bus tunnel, so they would be forced onto an Atlantic Avenue bus stop. Otherwise, this is like an additional Silver Line branch which serves East Boston residents from Maverick to Day Square. The main advantage of this route is that it could cut out a transfer for many residents of East Boston: instead of Blue-shuttle/Orange-Red, they could go shuttle-Red (and not have to add to the overloaded Orange Line). Another advantage is that it connects East Boston to both sides of the Silver Line. A disadvantage might be that it takes too long to travel from Maverick to South Station via this route, and therefore it is not worthwhile. On the other hand, it might be worthwhile just because it takes some stress off the central core (as an Urban Ring route might).
Anyway, happy to hear any more ideas, or if I missed something that makes these routes infeasible.