When Does High Sierra Reach EOL/EOS? I recently confirmed that Apple has dropped support for my mid-2010 MacBook Pro (i.e., I cannot upgrade to Mojave.)

Does anyone know when Apple will drop support for High Sierra? I'd like to know how long I have to come up with a solution before my MBP is exposed to security vulnerabilities.
From comments...

Best guess, another 3 years.
No-one really knows, but they tend to keep updating the last 3 versions. They claim 5 years active, 5 years passive support for any device, so another 3 years would exceed that.

MacSales supported OS list would seem to corroborate that - Mac OS Support Guide