Ok this may start a bit of a tangent and apologies in advance, but Rifleman brings up a point on incentives and office space.
Several Winthrop proposals are residential only, as MT has shown luxury high rise can fly off downtown. However, Boston has very low office occupancy rates and extremely high rents.
However, there also seems to be few companies that could really take up a huge portion of a large tower to get a developer going. That seems like it will only be more difficult since even if it is a large company, they don't need as much room for things like servers and systems that will at one time ate up a lot of sq. ft. Today's offices can be pretty lean and mean. Combine it with Boston's increasingly start up eco-system, there are a lot of fast growing, fast moving but still small cos in need of space.
Even in a hot market, these factors (combined with high construction costs) have made the spec office market very limited here.
I do not support tax break giveaways, but I would wonder in this environment that if Boston wanted to incentivize more office space here or a particularly neighborhood if they could do a sliding tax break based on the unoccupied sq. footage of a tower in its first 5 years or something. If the tower fills up with small companies quickly, Boston is out nothing. This would have the ancillary benefit of lowering or stabilizing office rent growth throughout the market and could keep or attract more companies to Boston. I am not saying do this for here, but maybe for more difficult projects (air rights, SST, Sullivan Sq., Roxbury) that have outsized social benefits for the city.