Why is VW still using YUI?

I was surprised today to find YUI code on my xenforo install. Its one of the reasons to move away from outdated and insecure vbulletin.

https://yahooeng.tumblr.com/post/960...-regarding-yui
Yahoo announced that YUI was outdated and dead in 2014:

Quote:

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Therefore, we have made the difficult decision to immediately stop all new development on YUI in order to focus our efforts on this new technology landscape. This means that, going forward, new YUI releases will likely be few and far between, and will only contain targeted fixes that are absolutely critical to Yahoo properties.

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Isn't it a better idea to move to jQuery?

We are not going to change the underlying Javascript framework outside of a major point release, since it would require every Javascript in VaultWiki to be rewritten. You must remember that VaultWiki 4 was first released in 2012 when YUI was alive and well. At the time, there were a number of features that YUI offered that the then current jQuery version did not, and they were features that we ended up using. Also, vBulletin used a significantly older version of YUI than VaultWiki does.

I should also note that the announcement of the discontinuation of YUI discussed a general trend which suggested the coming death of all Javascript libraries (which includes jQuery). The announcement talks about server-side Javascript frameworks being the future, but as a software developer, we cannot assume that small forum operators will have the option or the ability to install server-side frameworks. It may be a decade or more before these are considered "standard" technologies that shared hosts provide in a default environment.

It makes sense not to change a JS library outside of a major point release. However, YUI is dead and dependency on it will cause security vulnerabilities sooner or later. I know that's a challenging proposition and I do not know the answer to it. But I do think its something to think about. Maybe its something to revisit when XenForo 2 comes out.