I admittedly haven't looked at it since I gave up on my personal project, so I'm not entirely sure of it's state. However, a quick glance at the changelog seems to indicate that it supports .NetCore in some fashion.

https://github.com/apache/lucenenet/blob/master/CHANGES.txt

It'd be a shame if they discontinued it! A lot of incredibly smart and dedicated folks have put their hearts and souls into that project.