A friend Catherine sent me a couple of samples of a different kind of masonite panel. It is coated in a sort of enamel. I honestly did not think the paint would adhere well, but I wanted to give it a try, as she liked it alot.
It is maybe the slickest surface I've ever painted on, but, incredibly, the paint did adhere. It is a great surface if you want to do a wipe-off technique, as you can get back to nearly the white ground with no problem... It was actually quite pleasant to paint on. She sent me a couple more, and I'll give them a try also...
I do have a few reservations about long-term archival quality.. I will let this one dry and see if the paint has any issues with flaking off.. but it seems so far like it will be a nice option if you do not want to go through the trouble of gessoeing or oil priming your boards.. Stay tuned, and I'll let you know!