So what would be a less frustrating way -- tagging everything with as many (or as few?) keywords as possible, and then ad-hoc searches as looking through "virtual folders"[1,2] with the tag as the "folder name"? And more systematic ones as (SQL-style?) queries of tags with "AND" and "OR" logical operators? Or something else?
Yes - extremely rich metadata combined with robust search features.
For example: "I want to see all..."
- excel files
- that I myself have created (not downloaded)
- anywhere on my hard drive
- tagged with a particular project name
- containing a particular word inside the file
- sorted by "last opened" date
Then ideally you'd be able to save this search/filter/view for future use.
This isn't impossible to accomplish today, but it's so painful and slow that you're basically forced to fall back to folder hierarchies for organization.
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[1]: https://news.ycombinator.com/item?id=27916648
[2]: https://news.ycombinator.com/item?id=27916467