That's exactly what I mean...to a point.
To be fair, I fail to understand why they are using TBM at all. Building the city's third water tunnel, or a line under the rivers is one thing, but under Second Ave seems to be an attempt to increase the amount of time it will take to build it (and the amount of time lapsed goes up, so do the bills). However, they didn't ask me (Why is that? LOL)
Anyway, by provisions, I don't mean widen the tunnels neceessarily. That would be ridiculous. However, they could veer off the TBMs a little so there are curve offs for spurs to an express line.
I have to admit, however, that while at the moment it seems unlikely that express will be added. The plans laid out on the MTA's website, indicate to me that in order to build express tracks, the MTA would just have to build another set of tunnels along side the existing ones and reconfigure the stations that would become express (or the ones taht would become local) depening on how they wanted to do it. But given the projects already and nearly prohibitive price tag, we'd need a major policy shift nationally in order to do it. But hey, we can dream, right?