Yea that's why the switch needs its first revision by 2020 at the latest. Not because the sales will slow down or the first party won't be popular, but the third parties may no longer be willing to downgrade enough to get their games on the system. The risk of losing that support is essentially them repeating history.
But then again what seems pretty obvious is almost never the route Nintendo takes.
Revision or not they will still need to downgrade for it to work on the older models. Splitting the userbase by making it not work on the original switch is a bad idea so early in it's life.