Global abusefilters to expand the existing local filters to cover all wikis
The WMF hiring one developer whose sole job is to try to deal with the spam issue from a technical perspective, implementing captcha, writing extensions, etc. And in the remote possibility that a person with these competences would also be suitable for the job, general counterspam coordination.
All users who insert URLs need to be autoconfirmed or fill in a serious captcha
Hard captcha on account creation
Global checkuser, because it takes tons of times to track down spambots and it's a waste of time to CU one spambot locally when spambots have gotten wiser and now use the IP only per one account per wiki
True global block of accounts with autoblock on underlying IP
Assigning to global sysops the right to globally block accounts (no account locks, no global IP blocks) -- they wouldn't be doing much dmg anyway
Expansion of the global sysop wikiset to cover as many wikis as possible so that the gs who detects the spambot can take care of it alltogether: deleting the pages and applying the global block on the account or if it's not a gs who sees, they can get one
Spam and especially cross-wiki coordination of antispam measures as a topic at Wikimania, to convince administrators to report spam globally
Maybe even some extension or system by which if an admin is blocking a spambot, they get a nearby button to report it to meta with one click
More advanced blacklist options and functionalities
Aggressive rangeblocking of hosting farms globally
No more +cu, -cu for stewards to do before every single spambot check making people waste 10x the time it takes the spambot to edit to deal with it
Possibly even a global counterspambot group with broad permissions but with the clear policy that limits them to only act on spambots (that is, deletion of spambot created pages on all wikis, global block of said spambots, addition to the blacklist)