Rosen doesn't make sense because he only has 4 years left on his rookie contract. So if the Pats do pick him up, by the time Brady retires (IF he retires in 2 years) Rosen would be entering the last year of his rookie deal, which is never what you want, because you only have one year to decide if you want to lock him up long term.
The same thing kind holds for anyone the Pats would draft this weekend.
Brady says he wants to play til he is 45, I think he is a definite for at least another two years, so what really make sense is to wait until next year to find Brady's replacement.
Look at it this way....
If Brady goes down, the Pats are screwed anyways, so might as well "suck for Fromm (this year) or Lawrence (next year)" if that happens. Hoyer comes with a $1.5 cap hit if he is cut. All of that adds up to another year of Hoyer as the back up, and Ettling on the PS. Any QB taken say tonight would require you to cut Hoyer, take the cap hit, and he still would only have at most two years remaining on his contract when Brady retires.