In the late 80s there was a Betty Boop movie being tossed around Hollywood that was being considered because of the success of Who Framed Roger Rabbit. Eventually it got picked up in 1993 and production started to get rolling. It had full scripts written, VAs chosen, and animatics along with some early animation tests ready to go before it was suddenly axed due to a ton of issues with conflicting rights. Almost everything about it's been either lost to time or shoved in a storage shed somewhere in Hollywood, but this animatic along with full vocals for a musical scene has managed to make its way online.

https://www.youtube.com/watch?v=OiaodCj0pak