I would like to bring up the thread I wrote here: XCM as a Standard for Reading And Interacting with Parachains
I think that it totally made sense at the time of original Ledger Application development, to think of interfacing with Polkadot and Parachains via Pallets, since this was the only APIs exposed from the runtime.
However, as noted in my thread, the real long term, and scalable solution you all are looking for is an interface from ledger to parachain via XCM.
Then it would not matter which pallet is in the background being used for multisig, balance transfers, voting, or anything else. Also it will not matter when and how often these apps are updated. As long as a ledger device can produce an up to date XCM message, then any runtime should be able to interpret and execute that message as intended.
In this case, the ledger app developer just needs to stay up to date with XCM, which is a whole ecosystem need, and which costs can easily and fairly be split between teams.