re: So with the new redshirt rule, Brennan can play in 4 games without burning it...

You save Brennan until the last 4 games of the season. You don't want him to play a couple snaps here or there and it come back to bite you in the arse.

If burrow is still here next year then he can get his reps in then. It's not a priority to get him playing time this year. So just treat him like an old school redshirt until the last 4 games or until you have to use him. Whatever comes first.