One thing to consider, though, for any extension of any line, is that it automatically adds additional potential access via bus routes, either with or without reconfiguring lines. I know it's still a tough sell, but a shorter bus route to rapid transit is still a lot better than a long bus route to same.
On the one hand, though, I understand that this is not an area that many people would like to live in, car free. However, while I also see the risk in forcing new projects "suffer" to impose a future transportation policy that favors public transit, at the same time, it really is paramount that the system start changing itself now, and drive the needed changes. If anytime a development says, "this is too far from transit" we allow parking, that only perpetuates the problem.
The real question is: what are the barriers to development projects like this that favor cheaper housing and apartments, rather than overpriced condos? There are plenty of people who would choose to live out here be car free, and on average I am quite sure they tend to be less affluent. That's fine and those are the people who need housing the most anyway. I think we are missing the real issue here, which isn't really a parking policy question but rather a housing cost question. Simply put, richer people who can afford expensive condos dont want to live way out in West Roxbury without a car. That's fine, but maybe the real villain here is, once again, bad housing policy rather than bad transportation and parking policy.