Hello,
A more feasible proposal (than global blocking) which I've put forth before is crosswiki blocking. A Special:BlockCrosswiki page on Meta could be used by stewards to block a user on any project, preferably updating the log on that project. The interface would work in precisely the same way as the current crosswiki Special:Userrights, with a steward blocking "Pathoschild's_proposal_sucks!@enwiki" from Meta.
This doesn't have the problems of global blocking, and it would be extremely useful in stopping wiki-jumping vandals. Without crosswiki blocking, a steward needs to navigate to each project, register an account or log in, navigate to Special:Userrights and set admin access from Meta, navigate to Special:Blockip and block the vandal from the local project, and switch back to Special:Userrights on Meta to remove their admin access. By the time they're done, the vandal has hit six more wikis. Obviously, the current way we do things is ridiculous and not scalable in the least.