The api itself is a fantastic idea but putting it in a feature plugin as an intermediate step is nonsensical.

The rest api made sense as a feature plugin as there was a large number of people wanting to to use what was for Wordpress a very powerful new feature which everyone knew was going to hit core eventually

But the fonts api will simply be a better way of enqueueing fonts. That is great but won’t provide much incentive to test or standardise the api.

Feature plugins are great in some circumstance but not others