At least you can give the stylistic sets non cryptical names, although there is not yet a program, that supports that, even not the Creative Suite 5: Descriptive names for Stylistic Set ('ss01 - ss20') features.
And according to the OT spec, name IDs 256 to 32767, inclusive, are reserved for font-specific names such as those referenced by a font's layout features.
The name ID of ss01 starts with 256, as far as I remember. Just try, what happens, if you generate a ss21-feature with regard to the name ID, if feature params are set and if ss01-ss20 exist. I assume, that the AFDKO is already able to generate a ss21 feature with an individual name, although I have not checked that. So it probably is more a question of the missing apps, that support more than 20 ss-features, than a question of a tool, that is able to generate a font with more than 20 ss-features.