Thanks for this request. The problem for Audacity with VST has always been licensing. I’m not a lawyer, but the GPL3 option for VST3 looks more friendly than the terms for the VST2 SDK. I’ll raise this question with the development team.
If it is decided that we can support VST3, then I expect that VST3 will go fairly high up the “to do” list, though it won’t be for Audacity 2.4.0 (scheduled for release next month) or for the release after (as that is already planned for a specific major update).
Initial discussions with the Audacity team have been less encouraging than I’d hoped. As with VST2 it all comes down to licensing. Audacity is under the GPLv2 license (not “GPLv2 or later”), and relies heavily on multiple libraries that are not GPLv3 compatible.
The good news is that Audacity is becoming more “modular”, and the developers definitely do want to support VST3, so it is possible that VST3 support could be provided by a separately licensed VST3 module (licensed under GPLv3). Theoretically, this could even allow a closed source RTAS module to be developed, though I think it highly unlikely that would ever happen due to Avid’s licensing model.