When you say "wallboard"...Do ya mean drywall, or another type of hard panel? I've seen differing types.
*** Bottom line....YES, priming is a must. NO way around it. If you don't prime, bad adhesion will be a factor; along with uneveness of the desired "sheen", due to uneven absorption of the paint.
*** If using dark colors like Burgundy, you MUST use a gray primer, then 3 coats of the deep color.
*** Use top-line products for best results!
Thanks!
Faron