I don't think there would have been any additional capacity had the taxiway been extended to the 08 turning circle. It's a small backtrack now that can be done without increasing the gap on the approach compared to a departure from Bravo now.
It's more dictated on how quickly an aircraft can vacate the runway and without RET's (which won't happen) there won't be any further capacity gains in terms of runway movements until there's airspace and SID changes.