I wouldn't buy Coda 2 from the App Store before June 1st if I were you.
Source: the email Apple sent to all registered Mac developers in February.
Citation required. Can you back up that statement? Everything else that I've seen indicates that Apple will require apps submitted after June 1 to be sandboxed. I've seen nothing indicating they'll pull old apps.
Furthermore, what's to say they can't get custom entitlements? Apple is extremely eager to have every app sandboxed and has emphasized many times they'll work with apps who need permissions not in the standard set of entitlements to build custom entitlements.
I have a huge respect for Panic (specially for their taste in design) and I use their products, but not addressing this issue seems very unprofessional to me.