Alas, not soon. I want to take the next few months to add Android import and personal LAN use first. Then I'll think about porting. I am looking at Wine now though.
On Android, NoteLynX Pro has some neat ideas, including an outliner item having multiple parents, http://astrodean.blogspot.com/?m=1 Mindscope on iOS also allows an item to be soft-linked into multiple trees/parents for display, with a navigation path back to the original context.
ConnectedText on Windows, DevonThink and Scrivener on macOS have partial overlap.
For mobile: could doogiePIM import OPML files with dedupe? Many existing mobile apps can export as OPML. Could serve as a one-way sync/import.
For archival resilience: will the database format be documented, or could SQLite or XML export be supported? It's tempting to consolidate data into one app for UX/power, but we all know the long term risks.
For mail import, might be worth confirming that MBX import works from https://www.mailstore.com/en/products/mailstore-home/, a free (for individuals) German app that can archive email from many cloud services. Presumably doogiePIM stores email in a standard format.