[rustc]

There's no guarantee that a commercial license will be available at a reasonable fee, or available at all. You'll have nothing to negotiate with because the alternative is to rewrite or shut down immediately.

[InsomniacL]

Isn't that true of anything?

At renewal software provider X might hike license fees for Y to an unreasonable fee, or decide you're not worth the time at all.

I assume you can get a commercial license at any point, not only after you reach X revenue too?

[rustc]

It's true for proprietary software yes. The title of this post was "Gumroad is open source" (which has now been fixed).