From HN:

This article is clickbait and in no way has the kernel been hardcoded to a maximum of 8 cores. If you read the commit [0], you can see, that a /certain/ scaling factor for scheduling can scale linearly or logarithmically with the number of cores and for calculating this scaling factor, the number is capped to 8. This has nothing to do with the number of cores that can actually be used.

[0] https://github.com/torvalds/linux/commit/acb4a848da821a095ae9e4d8b22ae2d9633ba5cd