So it's not like all of the sudden all the Cab1L / Base1Ls and Cab2/Base2s all go poof. They will be out there and yes probably at a premium for now but eventually I suspect the prices will come down once folks that bought 5 or 6 start realizing they don't need them.
The list below with the exception of Cab1 does not cover the conventional options.
A Cab1 only communicates with a Base1 or original TMCC Powermaster.
A Cab1L (which is still cataloged) will communicate with a Base1L or Legacy base and currently and the Base 3 when released.
A Cab2 will communicate with a Base2 currently and a Base3 when released.
The current iPad LCS and iCab will communicate with a Base 1L and Base2 provided you have the LCS WiFi adapter. It is my understanding once Base3 is released they will also work with it.
My understanding also is that the Cab3 App will communicate with the Base1L and Base2 provided you have the LCS WiFi module. It will also work with a Base3 obviously.
The DCS App with a Base2 and LCS SER2 and TIU with cable will also run Legacy engines with almost all the full functionality of the Cab2. The DCS HH will run Legacy engines in TMCC mode regardless if you have a direct connection to the Legacy base or a SER2 / APP connection. When the base3 is released a SER2 will be required regardless of how you connect the DCS system. MTH R&D promises enhancements.
The 3rd party apps like High Rail and eTrain also can operate Legacy engines using the Base2 and LCS WiFi hardware. The High Rail app has almost all the functionality of the Cab2 with the added bonus of being able to program sensor tracks without physically touching them. A recent update provides tactile feedback for the throttle control. It's to be determined if they'll work with Base3 but I can't imagine why not.
If you already have a Cab2 then as far as a remote is concerned you are ready for Lionel's next leap in command control. I've had my remote since Legacy was first introduced and other than the first upgrade, never has been back to Lionel. With some exceptions they seem robust if taken care of. While I am not and App guy I can't wait to see what Cab3 looks like and functions. I know I'll have to migrate eventually so I want to be in early.
@Dave Olson please correct me if I have misspoken. All this information I derived from the various video appearances that Dave has made recently and some common sense logic.