Something I failed to realize yesterday about offering Secretary of State to Hillary Clinton is that it’s essentially a win-win for Obama. If Hillary takes the position, she’ll essentially be complicit in her political marginalization (at least to the degree a Clinton can be politically marginalized). If she doesn’t take the position, Obama will have extended the olive branch (though I seriously doubt there was a need to make such a gesture) and Clinton runs the risk of appearing ungracious and discrediting in advance any meddling she may pursue in the Senate.
As I’ve mentioned before, it would seem unlikely to me that Clinton accepts (indeed, the vetting process alone might be enough to discourage her). A better way of sequestering her might be a SCOTUS appointment.