Even if that were the case, it wouldn't have anything to do with the streaming service. Backwards compatibility would mean you could use your old cartridge's or disks. This is something that has only been done on three consoles, and now it's happening on a fourth, in a limited degree, with the XBox one X. Either way, even on all of those systems you still have to pay for the games. Even if the Switch were backwards compatible, that isn't going to mean the online service should then also be free for the game streaming.
Are you saying that games from older generations should just always be free on the newest consoles? Cause if not, I still don't understand the point you are trying to make.