Alright, I've banged my head against the wall long enough.
I'm officially giving up on my endeavor, and recommending the use of Kite's ups and downs for most ETs up to and including 31edo, with the exception of 30edo, and Standard Sagittal as it is for 30edo and everything above 31edo.
I note that with rare exceptions (7edo, 9edo, 11edo, 14edo, 16edo), 33/32 maps to 1 step of every ET in the ups and downs range, and the Sagittal accidentals for that comma conveniently share (simplified) ASCII characters with Kite's ups and downs. 7edo and 9edo don't really need accidentals beyond the normal sharps and flats; 11edo will almost certainly be treated as a subset of 22edo; and in 14edo and 16edo we might just as well say JI is irrelevant and repurpose the
symbols for "half of 9/8". Since I am skeptical that anyone is going to actually use Kite's ups and downs for anything much larger than 31edo (I suspect that users of larger ETs are more JI-focused and thus will be interested in the JI-related information that Sagittal accidentals convey), I propose altering standard Sagittal for the smaller EDOs so that they all use the
symbols for one step (in addition to the normal
symbols that retain their meanings with respect to the circle of fifths).
It seems like a win-win in that it a) retains a layer of pertinent JI information in keeping with the spirit of Sagittal, b) reduces the number of symbols needed to notate all the small ETs, and c) reconciles two notational standards in the range of ETs where they would be most likely to conflict, thereby facilitating communication among microtonal musicians using these ETs.
I feel confident that I have sufficiently explored other notational approaches to consider this compromise optimal for the vast majority of use cases.