Problem:
MobileFrontend works with any skins now if configured, but the mobile version of VisualEditor is only supported in Minerva Neue because of a hard-coded condition check. (See https://gerrit.wikimedia.org/g/mediawiki/extensions/MobileFrontend/+/67b269ee7297022405e94c7be142ade4594f2d6d/src/mobile.init/mobile.init.js#108)
Option 1. Introducing a new configuration value that is similar to $wgVisualEditorSupportedSkins. (Removed in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/VisualEditor/+/345207)
Option 2. Removing the skin check.