I would love having complete control over a site, even if it would take a long time to create. Like you said, some people will have their cause of making the website to learn HTML, CSS, Javascript, PHP, etc, and that is my main target while doing web development related things. Thanks for providing those links :)
If an update were to take place, I would suggest that we start at improving the overall security of Wikidot. 2FA would be a great start (to improve account security), then we could go from there (IP information for website administrators could be a possibility). However, like you said, the rate of activity on Wikidot seems to have declined; its peak was probably around 2011-2013. Overall, I think the main issue is security and being scared of what people can do. This is where we would have to add more security measures to handle spam/abusive users. There's also the problem of people wanting to create a website quickly and easily, which Wikidot lacks as well. Web building applications (let's take Wix for an example) are more popular because they look great, and can easily be made to look great (at little to no charge). Wikidot takes website creation in a programming approach, which allows a lot of customization, yet scares away the majority of people because it doesn't look like it is an easy approach. I personally like it because of easy, yet powerful customization it gives; I know where to change the CSS of my site, or what module to use to list members of a site, without having to modify x, y, and z folders (the drawback though is that I still don't have complete control, so this is a debatable topic). That brings me to another suggestion: add support for WYSIWYG website building (while keeping the programming oriented side of the platform as an option). I think this would attract more people to build their website on the Wikidot platform. Later if they're interested, they can get more knowledgeable with the programming side of Wikidot, and have even more control of their website. Both the programming and non-programming people will be happy.
And what is the application of SQL? From a little research, it seems that it's for business analytics purposes.