I also made a little decimal to Cistercian translator once. The numerals aren't in Unicode, so the font I use has to make use of private code points, which was kind of fun to get working properly. <https://cistercian.micahrl.com>
> It is not clear that there is any current need for Unicode support. Western Michigan University’s Medieval Institute (Cistercian and Monastic Studies) has a digitization project of Cistercian mss, but as of end 2020 they have not expressed any desire for computer encoding of the numerals. This document is therefore background information so that work is not duplicated if a need arises later.
Unrelated rant: The Unicode people have missed a lot more than that. There are an enormous amount of, for instance, musical accidentals that are missing, including ones that have been in use for at least a hundred years, such as the half flats or half sharps in e.g. Arabic or Turkish music, which are used by probably hundreds of millions of people in the Middle East. (They do have a symbol called "half sharp" and "half flat", but it isn't the same symbol.)
But at least they have the multiocular O, I guess.
If there's something missing from Unicode, you can propose it and there's a good chance they will add it to Unicode. Source: I got 7 characters added to Unicode.
The Bitcoin symbol is the most well known. Also the Group Mark from 1960s mainframes. The mask work symbol, like copyright for IC dies. And four half-stars.
Tengwar likely has to wait for the JRR Tolkien estate to release it to the public domain (CC0, for instance) or for the copyrights to expire on their own in a century or so.
(Same with Klingon glyphs and others.)
Such uses are probably fair use, but the Unicode consortium seems hesitant to test "probably" versus reality, especially since they would not see the brunt of the consequences but font authors and others might.
Unicode afaik focuses on taking already existing & supported character encodings, and incorporates those. Given there are 10,000 distinct glyphs, without some group of people already pushing for a specific encoding because it's what they use, Unicode probably doesn't have that strong a motivation to create their own (only to find out that it doesn't meet the needs of real users).
At least Unicode today doesn't need 10,000 codepoints to encode 10,000 distinct glyphs. Cistercian might make sense of ZWJ sequences of existing numerals plus a "cistercian mode selector". Authoring font ligatures to support that might not be fun, though, but also the cistercian glyphs are pretty simple concatenative structures almost perfectly designed for simple ligatures.
You're right, that does seem a better way to encode these—but that kind of encoding design I believe Unicode is wary of doing themselves. They seem to prefer sticking with a community-picked encoding instead.
Yes, I don't have an answer for that part and it makes sense of course, there's no reason to design an encoding that no one expects to use.
On the other hand, the above design idea (ZWJ sequences of arabic numerals with a "mode" marker) is offered free to anyone that does think they have a use for these numerals in Unicode and wants to turn it into a proper proposal.
Luckily Unicode makes exceptions for charsets/languages that are overlooked, also they take encouragement (via joining the Unicode Consortium) if you have a special symbol that you need to add for a private interest.
I also made a little decimal to Cistercian translator once. The numerals aren't in Unicode, so the font I use has to make use of private code points, which was kind of fun to get working properly. <https://cistercian.micahrl.com>