sometime my subscription list gets really big, and purging takes a good bit of repetitive clicking and waiting.  would be cool to implement a checkbox to select multiples to be able to delete many at once

We have that feature but unfortunately it doesn't work, at least for me.

At the top of your subscriptions list it says "click to open options and select community filters", Click on that

Click the box of the sub forum you want to clean out and unckeck classic subscribed threads, click submit

Check all of the threads you want to delete via the boxes on the left

At the bottom is a box that says "bulk unsubscribe from marked threads", click that

Doesn't work for me either.