And if someone wants it to work in the way that it does in every other VA plugin (ie velocity *adds* to the cutoff freq so that one starts and ends at a chosen level whatever the velocity)?If you want to avoid that a low velocity results in a cutoff value of 0, you can set Vel->Cutoff to a value smaller than 100.
Breaking with convention is fine so long as the result offers something at least as useful as the alternative - however, as with Curve's bizarre (sorry) polyphonic release for mono/legato patches, this is a case where abandoning well established convention yields results that are less useful.
Apologies if this comes across as overly negative. I appreciate that you've worked hard on Curve, and there's plenty that's good about, but the market for synth plugins is crowded and to have a hope of being competitive a synth like Curve needs to at least get the basics right.
All the best.