And what's the rationale behind this feature? Why would you need this, and most importantly, what is "half" a tick supposed to do? How should "half a tick" work affect frequency / volume / panning slides, note delays, vibrato, smooth MIDI macros, smooth parameter automation, etc...?

And once again, stateful effect commands that depend on surround effect commands are bad.

Well, something that I often see in modules is Axx commands applied like in my example above, and I thought that an "interpolated" playback of this would make it smoother.

It isn't exactly half-a-tick, that would be impossible, but what I meant was that each row would have five ticks, but the fifth tick of every odd row is shared as the first tick of every even row.

To enable this however, there would be a checkbox in "Song Properties", so people who didn't want to use it wouldn't be forced to use it.

Well, something that I often see in modules...