Not sure if I'm missing something, but making a list of businesses to reach out too I have ran into wanting to then follow up with then and manually add the contact info to my main subaccount. Would be nice to simply have button next to convert to subaccount to add contact details to a subaccount, and select my main subaccount.
Slightly more complex, Prospect Tool settings to set your subaccounts of choice to only show in the 'add contact details' button, so you don't get a long list of ALL subaccounts.