Currently when designing a product, you can allow the purchase of mulitple versions only if there are no add-ons and no editions.

However, it is very advantageous to allow multiple purchases for any edition. Need 5 accounts with access to the "beginner" level product? Done!

Also, add-ons are a bonus to any product, and allow the business to "walk the customer" over to a related and possibly essential companion. Retaining this ability to have Add-ons (even if only charged to the initial product offering) while still allowing multiple purchases is a win.

Bottom line: allowing multiple purchases regardless of other tweaks will be a help to sales more often than a hinderance.