> I tag each text file with topic, date and context keywords.

Nice idea. How are you doing that? Also, do you version control your notes?

> What does not work great is on the phone

I maintain an open source project called Dnote (https://github.com/dnote/dnote) which solves this problem for you. It's basically a command line notebook using SQLite + a mobile friendly web interface to which you can sync your notes.

Agree with you that we should avoid being locked into a proprietary formats or platforms. Businesses and platforms come and go, but our notes should stay as readily accessible as possible.