I really don't understand the mindset that it's slimy. I get the "rug-pull" thing, but just because you made a project with features a, b, and c that are free, why does that make it slimy to add paid features d, e, and f on top? People are still getting a, b, and c for free, so what's the problem? There's no rug-pull there.
Would it be better if a, b, and c never existed? It just seems like such a clear win-win to me.