19.10: Alt-tab task switcher in a standalone repo

Are there plans to publish the task switcher from 19.10 as standalone code? Or push it upstream and toggle with a setting?

Do you mean using Alt+Tab to switch windows instead of applications? If so, this is already built in. You can enable it on default GNOME in Settings → Devices → Keyboard and find Switch Windows, which has no shortcut set by default. Ubuntu just changes this setting in its default settings overrides.