Are there plans to implement a global CheckUser feature? I've seen previous discussion of the topic, but it's now 4 years old and there's been no progress. The value of a global CheckUser feature is immense, both for non-WMF sites and the WMF itself.
Often abuse isn't limited to a single site, especially if it's part of a larger farm or WMF project. Being able to see all accounts using a specific IP across all projects should help in mitigating abuse on the smaller projects where it would otherwise go unnoticed. Spammers using bots and other automated can hit several projects at once, and it would be difficult to detect the spam on smaller projects without many active users.
The more subtler spammers are difficult to catch too - those who insert external links to their own websites on multiple projects. While individually it may not be obvious, taken across all WMF projects it can be more easily spotted and removed.