There are more than 18 thousand votes: http://feedback.unity3d.com/suggestions/platforms-unity-editor-for-linu
and there is still no information from Unity Technologies if they will consider that or not.
It doesn’t matter how many votes are there. What matters is whether enough companies reach out to the Unity sales people and provide some idea on the number of license they would purchase. If the development cost Unity $1m, then it would be reasonable to assume that 1000 serial numbers would be purchased with Linux support. If you take a look over at the Forums you will see loads of discussions about this issue. Also, just because there are 18k votes doesn’t mean 18k people have voted. (Everyone has 10 votes, and you’d expect people who vote to be active Unity users. Any number of people can sign up just to make ten votes. Obviously on this particular topic, it’s likely that some people who create an account and vote are not active users, but we’d expect their Unity account to have real data in it.)