The Volpe campus redevelopment (MITIMCo) and the MXD parcels (BXP) are both Planned Use Developments, which means they have a master plan (which supersedes zoning) that specifies uses, heights, FARs, etc. Both of those developments are spec'd for one tall building each, with 121 Broadway being the one in MXD development and which has broken ground.290 Binney, getting close to topping out (8/29) from Discovery Cafe patio.
In my humble opinion, this area is very appropriate for much taller.
On that note - is there any chances for seeing more mixed-use between lab and residential? A taller hotel in this area is sorely needed as well. This building is too stumpy for me.