I got time to read and think on all this stuff.
I've written my answers on some ideas commented along this thread.
I've splitted what I don't like and what I think should be easy/powerful.
Please note I don't want to despise other people ideas, just share what I think are pros and cons.
- Lazy indexing
. it will stop suspend properly working so it would waste lots of battery
- Per-directory local global.db
. pollutes SD file system with files only useful for some corner cases
. SD cards don't like writings. I think this could reduce card lifetime adding more file system writings
. add more complexity to CTB... but (I don't think) benefits are not so big
- Search / file tracker
. basically it's the same that DR already has in its own DB
. could we implement a faster alternative? I doubt it
- Setting to disable indexing
. option to disable indexing each time system gets "card is mounted" signal
. also an option to run indexing manually
- A new file browser 
. not a CTB substitute, alternative browsing for advanced users or people with lots of files
. based on file browser paradigm
. could use its own DB to speed up searches
. integrated with DR (menu, toolbar...)
. DB could be populated/built from an external computer
 People who have read my posts in this forum since some time ago already knows that this is/was a project always on my TODO list.
In fact I already have an external book manager able to generate that DB...