Sox have added enough guys with catching experience than I'm not worried what happens with Gasper or Seigler TBH. I think Gasper is a great AAA culture guy, but really wouldn't want him in BOS too long.
If I had to rank the IFers on the 40 man, I'd have to do it in tiers.
Story/Mayer/Durbin/Conteras
KC/IKF/Casas
Monasterio/Romy/Eaton
Sogard/Seigler/Gasper
Cheng
KC - transitions to OF fulltime
Casas - transitions to DH fulltime
Seigler/Gasper/Cheng are moved off the roster at some point. Maybe Sogard instead of Seigler.