Dunno - the 96 Southwind we owned had the tv mounted high, not on the floor. But good cabinet shops could provide a lifting mount like you describe, if you are willing to spend the money.
Davis Cabinets is one such.
I haven't seen an aftermarket tv lift product, but maybe someone else has. Seems like it would have to be a kit, though, cause there are too many differences among Rv makes and models to do it one standard way.