Unless you're talking about a piccolo D/A, it should only be one musical whole-step above a C/G. Is it really significantly more shrill than a C/G?
Those metal reeds above G# on the right hand can really peep at you.
BUT you can really play a Scottish reel in A major fast with a box like Paul described above.
As far as the baritone row A is concerned, I don't know about that. I had an A-D melodeon but didn't care much for that bariton setup. Maybe it is just that I was used to playing G major on the C-G Anglo and wanted a box that duplicated it in A major.
Call me old fashioned, but I sort of like a 20 button Lachenol refitted with rivetted action. They really sound great with fine reeds. Nice, resonant tone. Light. Fun to wail on. I'll bet a G-D 20-button Lachenol would sound really sweet.
Still, D-A is practical. My opinion anyway.