We get feature requests and bumps like this daily. There is simply a practical limit on how quickly we can address features, so all I can say is hopefully we will eventually get round to it and I can't provide an ETA. It's already possible to do this with events (or third party plugin? haven't looked at it myself) so I don't see it as urgent, it's just a way to make something already possible a bit easier. Also I don't think this suggestion is as straightforward as you might think: ideally such a feature would be able to apply to any audio parameter, not just volume, allowing you to "fade" anything from the volume to a convolution wet/dry mix over time using a variety of curves (e.g. linear, logarithmic, cosine etc). Then there's the internal complexity of the Audio plugin which currently supports four audio APIs (only two are really relevant today, but we don't want to remove the old ones in case people still rely on them), and this makes changes a little tricky sometimes - it probably needs a rewrite or overhaul.
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