I have been roughly working this way since 2005 with DevonThink. I started by tucking things of potential interest and relevance into DevonThink and sometimes lightly annotating them in a comment (tags didn’t exist in DT then and they didn’t understand why they would be helpful). When DT added the ability to index, monitor, and update its contents by pulling in what is in and then what is new in a folder of text (later markdown) files that was incredibly helpful.
DevonThink has been brilliant for retrieving things from 3 to 15 years ago that are relevant to work, writing, expert witness work, mentoring grad students, etc. as much of what is gone from the internet around a certain subjects I have tucked away and searchable. I also have ALL of my ~70k PDFs, text / markdown notes, and documents in one DevonThink database (it shouldn’t work, but it still does).
About a year ago (June 2000) I put Obsidian on top of my text / markdown notes. Having the capability to interlink notes, drafts, presentation outlines, exploratory braindumps on subjects, articles, as well as concept pages and domain pages with booklists and notes on books and much more. I had more than 2k to more than 3k text / markdown notes (which DT had indexed and included in its own collection), but they were all distinct and not connected. Obsidian, over time has allowed me to interconnect these disparate ideas to move from one chunk of information to other related ones and synthesize new ideas. But, using tags I can easily aggregate concepts and ideas that have that tag on them. I use tags as hooks to aggregate and interlinking as bridges.
This works insanely well as I can now find what I am looking for much faster and make use of it far more easily.
The piece that is bumpy for me still is the crosslinking easily between DevonThink and markdown files in Obsidian. The issue is I work on my laptop and my iPad with Obsidian, but mobile DevonThink can’t work with my full DevonThink database / corpus. I have a couple techniques for connecting them on my laptop, but I need to pick one.