Sorry for commenting in the last minute---I just started implementing it and finally took a closer look.
I thought maybe-map would map proc to every value contained in maybe but realized it's more like the sense of fmap in Haskell Functor, correct?
I do see the consistency, but I'm not sure the value of providing *-for-each, *-fold and *-unfold full-set of sequence protocol, as they are trivially implemented. How much do we expect that Maybe and Either being used as a 0-or-1 length sequence?
My concern is that *-map family has been used for n-length sequences, and our Maybe/Either has multiple values, it can be easily confused users expecting srfi-189 *-map etc. are for mapping operations on each value it contains.