Why is it a risky move?
Because unless you have a regular backup strategy, deleting is a permanent operation. If you find later that you deleted users in appropriately because of a configuration (or worse, a coding) choice, there is no way to recover the data.
I started a MOD a while back that had the same intent, and I have spoken with kkroo about providing some of my code for this new effort, as it seems I will never be able to dedicate the time to getting mine done. The approach that I took was to run a script and populate users into a temporary table, then review them prior to deleting. Sort of a two-step approach, in a way, but it ensures that you get to actually look at each user that you delete.
Just me being paranoid.
kkroo may or may not decide to continue in the same way.