I ended up buying the Azek PVC beadboard planks. This stuff:
https://azekexteriors.com/products/specialty-items/beadboards/beadboard
It should match the house well, which is colonial in style with white siding and porch columns. I wanted to put the plywood up partially to provide additional sealing/insulating (I know, not much R-value), but mainly because I'm running the boards parallel to the joists in this specific application.
Hopefully I'll like this stuff and maybe use it on the other porches. Same neighbor I referenced used it for a recently renovated interior ceiling and he loves it.
Thanks for the input!