Good catch! The tricky thing is that Q2A supports MySQL 5.0 or later. But well, it makes sense to link to 5.7, given the circumstances. I've just created the PR to fix that: https://github.com/q2a/q2a.github.io/pull/49
BTW, I didn't know about that feature being removed. I can't think of any really slow query that could significantly leverage that feature in Q2A. However, I'm sure several plugins will be hit by this.
Sadly, the fix will either mean to use third party tools that might be a pain for the average user to configure or just write a programmatic cache in each plugin, which is the approach I usually follow (I've never relied in the query cache).