Doesn't the indoor section of La Hacienda de San Angel operate like this? While the serving lines are outside, I believe some of the indoor area is open for seating. I believe I heard that the cross-over happens around 4pm.
I presume that at some point they station CMs at the doors to keep new people from entering, they let people already inside finish and leave on their own, and if there are lingerers they probably politely inform them that they shoudl finish up soon and move along.
But you're correct that Be Our Guest will be the first restaurant to completely switch from Counter Service to Table Service.
-Rob