The risk I see with using DS in the name is Nintendo products, if you call it a NeoDS or similar there's the potential for people to get upset
My pick for a name would be to take on the competing NeoSD head on and go with a short name that tells you exactly what it is
My suggestions:
NGSD
NGM (Neo Geo Multi)
NGMC (Neo Geo Multi Cart)
NGMS (Neo Geo Max Spec) - not only a short name but combines multiple parts of the hardware title and tells you what it is, the maximum specification for a Neo Geo cart
Alternatively you could go with something silly
NG/Neo/Neo Geo Maxx/Maxx Spec
Salt Bae presents Neo Geo
I Can't Believe It's Not NeoSD