Guest customers under one ERP account!
Today every guest customer is saved as separate account in ERP and this generates thousands of accounts never being used again - pretty busy.
Instead i propose that for guest customers one account e.g. "Guest Customer" is used and every customer is saved as new contact under this account.
This avoids creating unnecessary accounts in ERP which is pretty critical issue.
If only obstacle is returning guest customer with same e-mail then rules are simple - it creates new contact every time or option is to push order to already existing contact if all fields are filled identically. In any case contact is not something affecting ERP reports and finances so much as accounts. Having tens of thousands of guest accounts will mess up customer database in ERP sooner or later.