How about a video crossfade button..............
 

I just thought about the suggestion from my previous post. Maybe you can add a "crossfade play" button that would be operational when a second instance is open and instead of hitting "play" would hit "crossfade play" and the video on the secondary monitor would crossfade from player instance one to player instance two.........maybe add a selection of fade or wipe types to chose from before you make the fade.....If this needs to be in the pro version it would certainly be worth the price......If you did this feature I would even be willing to be a sales rep for you as thousands of Dj's would buy this if the price was right 'cause there is nothing on the market that will do it.