I use vMix Replay as a separate external replay system, using the two external outputs to feed my A and B outputs into a router/switcher.

Some directors like to mix between A and B themselves, but others prefer you to use A and B like Preview/Program, and while B is live, be able to 'push on', mixing to the next clip you have prepared in A.

I have previously used the Newtek 3Play, where you could hit the 'take' button, which works like the ReplaySwapChannels button does currently, to swap the A and B channels around.

The 3Play also had an 'auto' button, which would swap the two channels using a transition of your choice.

I appreciate this is no simple task, and there is already a transition system for pgm/pvw in vMix, but the option to have a simple fade between the two channels would be a huge improvement to the workflow.

Perhaps it could be fixed for now, and customisable in the future. 18 frames was my duration of choice!