Yeah, a little odd - never really thought about it though. I'm sure you could pull together a quick script using the API to do it though Blake, just use the merakiAuthUser end point and a module to read a CSV file. How hard could it be.... (okay its not simple, simple, and yes, an import CSV file button would be easier).
EDIT: Just thinking, most RADIUS servers allow you to create groups to test against, so that would be one way too. LDAP is a bit more problematic unless you can move all the users you want to be able to authenticate successfully to a separate container - not an ideal option in all circumstances.
