Realistically, since there are only 2 crew.... and the crew ONLY fly aircraft that are 2-crew aircraft there isn't any point in getting into the routine of "Arm & Crosscheck" announcements.

Mainline crews are all cross-qualified to work all types and they could (in theory) be on widely different types from day to day and a significant number of those aircraft would need the announcement.

Maybe our famous SD could chime in.....