Yes! “attempt to call upvalue 'isfile' (a nil value)” was the error that would break compilation after I updated this morning.
I’m not entirely sure why the format-generation problem is preventing installation now, whereas this morning it updated successfully but wouldn’t run—but I’m glad you can reproduce the error.
Given that at least in some situations, attempting to install the texlive-binaries package currently in testing will cause apt to hang, this seems like it could be a fairly serious problem.
—TK