On-deck means the player is ready to jump in when called, and this urgency is very important in, let’s say, a tournament running on a tight schedule. During mixed, I was saying “please get ready now”, because when people hear “on deck” they think “oh, i have some time until next game starts”. Maybe “by-the-court”, indicating that the team should be ready watching the previous game finish? Along-the-boards also has a nice ring to it. To reflect this urgency, I would also change in-the-hole with something like “playing next”, even though there are still two (very short) games to go.
I think every tournament should strive to let people play the most games possible, and consequentially making the teams change as smoothly as possible is paramount.