From what I see int the list of existing tracks, de facto , for numerical versions it’s just the number, so in Saiku’s case it’d be 3/4, if they want e.g. the “3” track to contain versions 3.x, and the “4” track to contain 4.x and so on.
Most tracks are for software which wants them per minor release (e.g. Go has 1.7/1.8 tracks).
It can also be a string as in the case of Openstack which is trackified by series name.
v3/v4 looks weird to me, so I’d suggest 3/4.
I am, if they are in the “store” category. Was this request filed there originally? I’ll try to pay closer attention to these requests, or feel free to ping me directly if you see one that’s been hanging around without reply.