Can h22 paint in all PBR channels as the karma renderer updates during painting or is it mostly for simple color sketching like shown in the keynote?

Being that, unless I am mistaken, Copernicus doesn't really manage it's maps/channels in the same way that Substance Painter does, in terms of painting directly to certain channels, etc - it's likely that no, it won't paint to PBR channels in the same way. Instead, it'll be up to you to determine how you use the paint feature to refine the maps you have and then use the data to create the maps.

I wouldn't be surprised if there are some recipes and examples that could be tweaked. H22 seems quite recipe friendly.