Problem: Currently all global blocks always block account creation. Stewards can only choose whether the block will affect unregistered or registered contributors (the so-called softblock or hardblock).
Proposed solution: In line with what happens with Special:Block, please add a checkbox to Special:GlobalBlock and give stewards the option to check or uncheck that box depending on the circumstances.
Who would benefit: Stewards as users of the extension; but all users too as we can allow account creations in case where the abuse exclusively comes from unregistered contributors.