What is a surprise, though, is that I am seeing a lot of new rifles coming onto the market chambered in .325 WSM in the last year. Anyone know why this sudden resurgence of the forgotten and niche .325 WSM?
Nope. The round is as dead as the proverbial dodo bird. What you're seeing is mfg's clearing out rifles they couldn't sell.
The 325 was a dumb move... Olin should have legitimized/standardized the 338 WSM. The 325 does nothing the 300 WSM didn't already do, and do better.