I like wood ceilings, especially installed on the diagonal.
the diagonal really shows off the wood & adds to any room IMO. however, when you do wooden ceilings inside the conditioned space, you should be aware of how much air leaks through them. even t&g wood.

the way we deal with this situation is to put housewrap on
the ceiling joists, then install wood on top of housewrap.

I first encountered the excessive air infiltration when testing
homes in an upscale subdivision. builder was known for the beautiful wood ceilings in his homes. however they were expensive to heat/cool, so I was called in to do some diagnostic testing. the ceilings were the issue, as they allowed excessive amounts of hot humid air from attic above to enter the house/room.
not much we could do, after house was completed & attic
insulated.
but from then on, builder would use housewrap first, then
beadboard on top.

I've done this same install, beadboard on diagonal in a guest house for BIL. cathedral ceiling, housewrap, beadboard. beadboard was clearsealed so that wood could be seen. really beautiful, and with the air barrier made by
housewrap, the leaky individual boards were not an issue.

back to advice from others, just wanted to let you know
the problem with these types of ceilings & the easiest
way to address them.

best of luck.

Thank you energy rater. I asked my husband what he used in the den as a barrier, besides two layers of insulation batting (laid in different directions). He said a heavy duty plastic. He also said he'd do it differently if he had to do it over again...I've already forgotten what he said he would use :o Anyway, as for the wood ceiling in the bathroom, he would be leaving the existing sheetrock as a barrier, provided it won't be a problem with the Panasonic vent fitment.