There are only 8 single-level diners in the regular daily service at the moment: Silver Meteor and Crescent. (Yuck.) There's one Viewliner diner in service, #8400, so they have to bring out 7 in order to replace the existing service fleet (most of the time, apart from maintenance cycles). Although we were told more than once that the LSL would be the first recipient of the new dining cars, I'm afraid they might replace the Meteor's dining cars first due to the location of Hialeah. :-(
Most likely some Heritage diners will be put into protect service initially until Viewliners are covering the full load (Meteor, Crescent, LSL, and perhaps Star and Cardinal as well). There are apparently 11 Heritage diners active as of early September. 3 are ex-Northern Pacific, 3 are ex-CBQ, 1 is ex-BN... there's 1 ex-SP, 2 ex-NYC, 1 ex-Pennsy (#7143, with a really crazy history of multiple conversions). I suppose they're probably be retired as their "need new inspections" (of whatever sort) dates come up, which I don't know the order of, but if they have to renew some of them and keep them active, I'm guessing it won't be the NYC diners which are from *1948*. (I'm surprised they've been kept going this long, and I'm also surprised that the many-times-converted Pennsy car is still going.) There seems to be a preference for the BN/NP/CBQ fleet (which was all pretty similar as those companies were quite incestuous).
I will say that if they manage to get #68000 and #68001 in service along with #8400 and they manage to get Chicago and New York trained to maintain the new cars, as well as whatever "training" is necessary for conductors and engineers, they could equip the LSL. That's the only one they could equip with that few cars. So if the two "prototypes" are finished and then there's a long delay before #68002 comes out, there is a possibility of the LSL seeing the Viewliner IIs and everyone else waiting for the mass production.
The LSL used to get half its diner patronage from coach, IIRC, the highest of all the trains with dining cars. Not having a proper dining car on the LSL is throwing away revenue. I hope they did it so that Chicago didn't have to maintain Heritage dining cars at all any more, which is a reasonable reason which might outweigh the thrown-away revenue. But it would make sense to restore service to the LSL before replacing the cars on the Meteor. (On the other hand, making it so that New Orleans doesn't have to maintain Heritage cars would *also* be a reasonable reason, so replacing the dining car on the Crescent first might make sense...)