As long as this continues to be the state, city, and BRA that can't keep two hands off their own necks parceling off golden Pike air rights real estate that have been available for sale for 40 years, I think 2040 is wildly optimistic for Widett decking sans Olympics. Why in a rational world would there be developer interest in floating the up-front costs of any decking in an all-new district that itself is going to take decades to fill when every Pike block from Back Bay to Albany has yet to be filled with developments that instantly knit each South End block together...with MassHighway picking up considerable chunk of the decking cost.
That is not a winning sales pitch to developers even if the non-Olympics up-front costs came way down. They're just going to point at the more instantaneous profits to be had in literal eyesight of Widett on the other side of the South Bay interchange and say "Why not there? What the hell are you waiting for?" And 40 years of public authority FAIL won't have an answer for that. Which means they don't have an answer for why Widett, and why up-front decking cost is worth any developer gamble on a deep long-term growth new district. Should any private entity have any confidence that delivering the bare canvas is going to get the public partners they have to engage moving fast enough to fill that canvas? Swallowing that up-front cost means they have to know when it'll be amortized. 20 years? 40 years? Or Turnpike Authority passing in-and-out of existence years? What's the BRA going to do there to stay out of its own fucking way in ways they most certainly haven't done elsewhere?
They know these are the hangups that are going to make developers overly skeptical of taking on the challenge. Why else are they sticking to their story of Midtown-as-monolithic-build Olympics or no Olympics? Because they know it's not happening piecemeal. They stare every day at what they have not been able to accomplish moving valuable air rights real estate. It has to be a master developer baited into building the whole neighborhood, or it's just not going to happen. And I don't see any profit motive for a master developer signing on to build the whole neighborhood, because they'll never have complete enough control over their timeline for amortizing that up-front cost as long as they're still non-optionally bound to dealing with those same old public authorities--City Hall, BRA, MassDOT--stirring the pot about what goes there. It doesn't even matter if a master developer has the upper hand; they want guarantees they can pay back the up-front costs in X years, not X years + Y years in delays because the public stakeholders were being their usual slow/squabbling/disorganized selves.
It's Olympics, or the whole plan gets mothballed for retooling. If it gets mothballed for retooling they turn their attention to Harvard and Beacon Park, Fenway, Seaport, Suffolk Downs, and etc. Because they have to. There's no excuse for wasting energy and planning resources creating brand new districts whole-cloth when their existing brand new districts are still under-full on land use, and planning sloth is one of the chief culprits as to why they're lagging (or in Beacon Park's case, will lag) under-full on land use. That doesn't mean nothing will ever get built over Widett/Midtown. It does mean it'll cease to be relevant discussion for another 20 years...minimum. Because there won't be enough profit motive to bait a developer with the up-front costs for another 20 years...minimum.
Thus, they're banking on a hole-in-one or nothing at all. If they don't win the Olympics, they'll make their save-face show of "we're still doin' this, I swear!" and then it'll quickly fade. Then resurface every couple years, then fade again. Life will go on. Building in the city will go on. Ground-level activity at Widett will go on, whether Food Market continues to be tenant or not. Certainly the various transportation interests down there--MBTA, BTD, and Amtrak--are at no loss for immediate productive uses or chess moves for dibs on space underneath possible future deck. But no Olympics hole-in-one = no fully-grown Midtown before our grandchildren come of age.
(EDIT: ^^West^^ beat me to the post button on a lot of this.)