What are the impacts of implementing a hot-desking model for grad student workspace?
I have seen hot-desking (or the equivalent) work well with undergraduate researchers. In the particular incarnations that I have seen it, however, it wasn't a large-scale formal hot-desking model like you're talking about, but rather a sort of "pool office" that was the shared space of a bunch of undergrads.
With the undergrad researchers, this worked well because the number of hours each student typically spent in the office was quite small, and they tended to work on projects for relatively short periods of time. 

Graduate students are a different matter. They tend to be around for a much larger fraction of their time, and you want them to be in the office more and to develop professional networks and commitment to the group. Thus, I don't see the advantages of hot-desking for undergraduates translating well to established graduate students in most STEM environments.  Here is a report of a personal experience that seems to corroborate the problems.

That said, there are some environments where is seems like it could be appropriate, in which one does indeed expect an office space to be transient and sparsely used.  For example:


If students spent most of their time in lab, then their "home base" is their lab bench, and a hot-desking space for non-lab tasks could be workable.
Some graduate programs start with a year of "rotations" in which students work with a number of different groups before committing to one, and since rotation students are inherently transient, hot-desking might work for them as well.


This all seems to point to some potential metrics, along the lines of measuring how much time is spent working in the hot-desk space vs. how much of the tasks done in that space are being done elsewhere.  If students are elsewhere because they are doing different types of tasks, then it might be guessed to be succeeding; if they are doing the same sorts of tasks in coffee shops, libraries, etc., then it might instead be driving them away.