@eniatitova I don't know enough background, and this page says it has outdated information, so I don't know what's outdated. But it appears like at one point the plan was to combine the L & K lines so an LK Service would run from Taraval to Ingleside, and the only route that would go through the tunnel would be the M.
https://www.sfmta.com/projects/west-portal-lk-transfer-project