I have a private portal where I have more than 50 users. Having to copy/paste email addresses and names that many times, stinks. And this won't be the last time I want/need to add a bulk set of users.
Good news, you can already import idea portal users using CSV. If you go to Settings -> Product -> Import from CSV, one of the available options is idea portal users.
I am going to request that a link is added to the idea portal users management screen so it is easier to find this import capability.