>>The application does not have to worry about which data back-end is being used.

Of course it does.
Data management is what we do.
It's our job to be sure that we give the client the best possible way to store and access data.
I won't forego modern capablities in order to remain compatible with obsolete technology
I'll support the obsolete technology, but I won't let it limit me.
The only answer I can see is two code bases.