Hi @Will_Cervarich , great questions!
For the accounts question, disabling the account does not unlock the merge feature. The account, while no longer connected to that profile still exists and the customer could reactivate the account at any time using the same email address. I believe this is the only permanent blocker at this time, whereas the other ones can be temporarily removed and re-added (metafields) or their gift cards, etc, can be used up. You could also cancel gift cards and reissue their remaining amount through the correct account if you wanted to clean that up sooner.
The discounts on customer profiles is most likely referring to wholesale account discounts, which is a PLUS feature.
In regards to: if we have two customer profiles who’ve both made purchases and aren’t otherwise blocked by any criterium on your list, should we be able to merge them?
Yes, you should be able to merge those two accounts. The current issue with merging customer accounts with credit cards on file might cause this to not work at the moment, but that issue will be resolved ASAP.