Hi @jwdebelius !
These palettes look great!
Same with all the existing palettes — so I would be in favor of adding the palettes first, then attacking the collapsing issue second.
I'd recommend sticking with the existing action instead of writing a new plugin, to leverage the interactivity and other features. I don't think that starting fresh will necessarily save time here...
In theory yes this should be possible, and there are a few related open issues in q2-taxa (which is to say that if you want to tackle this our children's children will sing your praises)
An "easy" way to approach this (compared to the hard way of getting vega to do the collapsing interactively inside the visualization), would be to expose an option in the action to collapse low-abundance taxa before visualizing. The action already collapses the input feature table at each taxonomic level — such an option could further collapse these tables before saving as CSV and passing to the visualization.
An enhancement on that would be to save separate CSVs — collapsed and uncollapsed tables at each taxonomic level — then in the visualization you could add an option to choose which table is displayed (instead of dynamically collapsing the table inside the visualization, which would be really awesome since you could do things like interactively select the abundance threshold for collapsing, but probably a lot of work to implement).
Just exposing the option would be a low-tech way to accomplish this, and much less work than writing a new visualization. Curious to hear what you and others think!