Six cities set up regional planning effort, bypassing existing regional planning effort

What about the respective City/Town Councils/Alderpeople ?

http://www.cityofboston.gov/citycouncil/
http://www.chelseama.gov/Public_Documents/ChelseaMA_BComm/council

http://www.cambridgema.gov/ccouncil
http://www.somervillema.gov/departments/board-of-aldermen

http://www.townofbraintreegov.org/towncouncil/index.html
http://www.quincyma.gov/government/CITYCOUNCIL/

MAPC might be awesome

It is pretty great - they produce some real interesting reports, they're one of the few agencies that takes an appropriately scaled view of policy implementation (that is to say, Metro-level), but....the MAPC is a solely advisory body. There was a great push for regionalization of services from the 1860s up through the 1930s: it birthed the MPC (prior to its gutting for patronage), metro utility organizations, the Boston Transit Commission which provided the political impetus and wrangled funding for BERy's rapid transit build-out, and the annexation of Rox, Dot, Brighton, W. Rox, Charlestown, and HP by Boston (mostly as rapid population growth in those areas overwhelmed the ability of municipal governments to meet the demand for modern infra and services).

The major policy area that never achieved regionalization...land use. Land use is still the primary power of municipal governments and one of very few areas where local powers have not been superseded by the State. As snazzy as the MAPC's reports are - they're talking into the wind; the MAPC's power of implementation is almost entirely nullified, with some, indirect, exceptions. This new agency holds potential, but is going to suffer that same lack of bite that MAPC lacks. But if we're being optimistic, here are the good things:

1. Cambridge, Somerville, Boston, et al have similar economic and travel pattern connections. A lot of the MAPC towns are only marginally wired in to the core economy, but these six cities are irreconcilably connected to Boston so there's the ability to craft a more detailed plan.

2. I think we're finally past the era of Boston celebrating the businesses it attracts from far-off lands....like Cambridge (cough Vertex). 20, 15, even 10 years ago, each town was reasonably more concerned with development within its own borders; today, the policies with the greatest impact on Cambridge's housing market are being developed in Somerville, Watertown, and Arlington. If this organization furthers that sentiment, then that's a success in and of itself

3. There's still of ton of areas to work on just within these core towns. Quincy/Braintree are locked into to Boston's economic sphere with only a paltry connection to Cambridge. Chelsea is the same. Somerville is the only town on this list that has parlayed access to both economies and I think it's little surprise to note that Somerville has been able to craft far more substantial changes in the last 20 years than any other city in Mass. Greater cooperation between Quincy and Cambridge, improved transit links between Chelsea and Cambridge could have very meaningful impacts and regional, but focused, body is probably the best place to develop and advocate for those policies

4. Or pessimistically, this turns into a bunch of people with BIG IDEAS talking to other people with BIGGER IDEAS and nothing meaningful happens. That's always a possibility (probability), and especially so considering its just an advisory board. But I do think there's a lot to be said for treating the core as one function unit - it's kind of ridiculous to have 6 different redevelopment authorities covering an area that is smaller than many American metropolitan counties - it's politically useful, but inefficient and wasteful.

The "goals" referenced in the City of Boston news release seem are pretty impressive though, I think (hope) there might actually be some legs for this one.

EDIT: Just to flesh out the question "Why have a new body and not the MAPC" a bit more. The MAPC has a Federal role, its the organization through which Federal initiative grants are programmed, many of which have a basis in environmental resiliency. That's why the MAPC often couches many its reports' recommendations in environmental terms (as is also the case with the MPO). The GBREC seems to take a more functional, econ. development approach - both of those are parts of the MAPC program, but they exist in a complex relationship with environmental goals. That's what I mean when I say that a more "targeted" approach could be beneficial - environmental degradation is often a symptom of structural issues, so addressing negative environmental externalities can get be like papering over issues rather than solving the core problem. I'm not saying the GBREC will solve the core issues either, but its scope seems to be less tied to meeting environmental goals which give it more flexibility in the long term (and could have a greater impact on quality of life/issues of convenience)) should the partnership work out.

yay more money spent on "consultants" or "contractors"

/s

From what I know from friends who have contributed dogs to this hunt, they probably actually intend to work together to actually do stuff, rather than study or talk about it. The larger reason is that Boston tends to lag in political will to implement data-driven and forward-thinking changes and doesn't work and play well with others.

Too bad this has happened during Medford's mayoral transition. I hope we can get a piece of it as well.

....hence the need to create their own organization.

mapc just covers too much area to be useful, like the mpo.

Don't know if they have specific duties or weight regarding NEPA/MEPA (never had anything to do with MAPC in those contexts) but regarding transportation planning and the Boston Region Metropolitan Planning Organization (MPO), MAPC provides some planning assistance and sits on their Advisory Council.