Congratulations on the fantastic updates on Indigenous! The recent changes are making me wonder how I’ve lived all this time without it.
My first use of the read post functionality was a tad confusing because I wasn’t aware that either the WordPress Micropub client or Post Kinds supported the read-status set up that IndieBookClub.biz had pioneered.
The vast majority of my read posts are for online articles which are relatively short in nature and so don’t use the read-status features and are simply marked up with read-of. When I originally suggested that Indigenous support read posts, I only expected the read-of support and didn’t imagine the additional read-status support for “to-read”, “reading”, or “finished” to be included. These are highly experimental and have thus far only been supported by IndieBookClub which focuses on much longer book-length content that can take better advantage of the ideas of the idea of a bookmark to read, ongoing reading, and finished reading markers. Even with this support gRegor still thinks that it may be better to use the addition of p-category or u-category microformats instead of the read-status tags. The WordPress Micropub server is the only other software that supports these additional read-statuses besides gRegor’s own website.
Given that:

an exceedingly small number of sites have support for read-status;
the read-of microformat has somewhat better support (though it is still an experimental microformat itself);
the majority of posts that Indigenous users are likely to use for creating read posts will be articles (as opposed to either smaller posts like notes, likes, favorites, checkins, RSVPs, etc. or book length material),

I would recommend that you have a default setting in Indigenous for just read-of without a specific read-status (the UI could either indicate “none” or “read” without a read-status value). However for the occasional longer form usages leaving the other options in would be useful. I can easily imagine myself using the option for “to-read” over the simpler bookmark functionality now that it exists!
Thanks again for all your work!