You seem to be a bit confused. The 1200 and 4000 share a chipset, the 3000 is closer to the "original" chipset but they're all the Amiga chipset, just different revisions.
Your typical 4000T with a Mediator, Radeon, PPC/060 etc wouldn't make use of Paula and friends in day-to-day usage.
In otherwords, how many RTG users run WB (and WB applications) in AGA

It would have made more sense to ditch the old planar chipset for the 3000/4000 and gone chunky RTG instead.
So to get back on topic, a super fast accelerator for the 4000....yes please, for the 1200/600/500 then no thanks.