As I see it, the expectations I'd have towards a mobile note-taking tool (like Google Keep) are different enough that I think it should be a separate program. Folder structure would be fairly cumbersome to navigate on a cellphone, and few keyboards make it particularly easy to type the symbols that control Markdown styling; on the other hand, you'd probably really want solid support for shopping/TODO lists and the like, for which Google's tiling organisation paradigm seems very useful.