busses don't work from the MAT. it is too long and expensive.
AA doesn't want a split operation. Neither does DL.
DL might well be willing to trade something strategic in other locations, hint, hint, in order to make things easier for AA/US and other airlines at LGA.
All the indications are that the LGA-BOS mainline 717 operation is working very well... all the reason for DL to do the same thing with the DCA-LGA leg of the Shuttle and for AA to realize the value it could add to the LGA-BOS leg for AA.
Unfortunately, AA gets little value from the LGA-DCA with the rest of AA's LGA operation because AA has few flights to destiantions north of LGA.
but this is all about LGA.
at JFK, DL is in the process of further consolidating into T4 which is way better than T2 or 3 and then start renovations on T2 as well as add a couple more mainline aircraft gates where the regional carrier operation was until a couple days ago.