@murathan, my good fellow, accordionists have no requirement for the term "niche".
It may seem to us like some accordion designs are more (or less) "niche" than others, but the reality is that to muggles (non-accordion folk), we are ALL as niche as Mr McNiche from Nicheville, Tennessee.
It doesn't matter if you play an inverted Z griff button accordion made from Cadbury's chocolate buttons or a Kravtsov carved from Crunchies - the rest of creation would not blink an eyelid.
P.S. Obviously piano accordions are not niche at all - we are part of the greater Universal keyboard system.