Completely - they simplify the act of transforming data into visualizations down to the essential association of dimensions to axes/color/etc visualization concerns.

Absolutely with you.

Visuals defined in JSON (so perfect for manipulation and generation) and also able to bake-in custom interactions within that is an awesome power.

I like the look of Observable Plot, but it doesn't do interaction like Vega/Vega-Lite. (They are working on some interaction though, and they have quite the team)