Alright, I get it. Non-4/4 time signatures are in much higher demand than I originally thought.
* edit - I'm not trying to sound mean. I just want to make it clear for those who may have not read my other comments on this HN post.
I thought it was clear that these non-features are only for the MVP, not the released "1.0 version", but apparently I was wrong. The "final" 1.0 version will indeed have support for other time signatures. Although because demand is apparently very high, I will likely add it to the MVP as well.
The way I have this designed, it is in fact trivial to add other time signatures later. The backend code only uses musical time as a unit of beats, it does not care about measures. Measures are purely just a visual thing for the GUI. Yes there are special plugins that care about measure like drum sequencers and advanced arpeggiators, but neither of those things are planned for MVP, so it's not like we will have to "rewrite" them.
What is not trivial to rewrite is support for non-western scales and microtonal stuff, which is why those are being included in the MVP.
The title of this HN post was updated, it now has correctly removed "fully-featured" in the title. Neither I or anyone on the Meadowlark team made this HN post. We got publicity a lot sooner than we thought we would, so we weren't even fully ready to make a full public announcement on the project yet. The design doc is still somewhat of a draft.