Is this New York state, under the IPC, or NYC, which might have different requirements?
I only glanced at the first drawing, but looked more closely at the second drawing. Seems like the second drawing doesn't eliminate the vent stack, it just moves it farther away from the soil stack. A few more comments based on the IPC, some of which may duplicate Tuttle's:
- On the upstairs showers, I assume you dry vented them rather than wet vent them, as the latter would require dropping the traps to line up with horizontal drain under the joists, which would make the bottom of the trap extend lower than the horizontal drain. You could consider running each shower trap arm through the joist directly to the soil stack, as nothing would be draining in above them, so the stack could vent the shower trap arms. Either via stacked san-tees, so the two traps would be at different heights, or with a 4x4x2x2 sanitary tee with sanitary side inlet, if such a thing exists.
- On the downstairs WCs, the lower (on the page) WC can be wet vet vented by the dry vented upper (on the page) WC. That would eliminate the separate dry vent takeoff for it.
-If you're concerned about the 2x2x2x2 double fixture fitting for the lower showers, you could certainly plumb them with separate san-tees like you show the upper showers.
Cheers, Wayne