My comment is partly about priority sorting (as mentioned here), but also in general is about the overall search UX so I started a new topic in the hopes it generates more ideas.
In general I think most of the features for search that I want are there, but they are currently tough to discover. FYI, my notes are based on the iOS version of the app. Obviously I'm just throwing out some UX thoughts based on my other experiences working on search UX (work on search in my day job). I'm sure I haven't thought of everything, but I hope this helps.
I very much love the saved searches feature, but it is tough/confusing to navigate them. I think a better UX would be to think of the TODO tab as being a list of the potential searches that could be done. Maybe the icon should even change to be a magnifying glass since this this tab kinda serves two purposes. When a user has not upgraded to saved searches, then the main screen contains a list of different states to filter by. When the user has saved searches, then the list would also have any user defined items. I think it would be good to also allow the user to manually order the list of saved searches (the pinning you have recently implemented in the files tab is ok, but dragging the ordering around would be nicer in both places IMO).
The TODO tab would still have a search box at the top, but below it would be the list of these filters/searches. If a user starts to actually search, then that would show real search results, but there would be a prominent back button at the top to exit the current search and return to the list. This would be the same mechanism for any of the saved/default searches. The user clicks on one, sees/interacts with the results, and there is a back button to go back to the list. This really isn't any more clicks than currently exists to switch between saved searches, but I think would use up less screen space and make navigating cleaner. The current pop up for saved searches really also won't scale for more than 10 or 20 very well.
In addition to a better UX, I think this UX would give you a more prominent placeholder for an upgrade call to action at the bottom of that search list (the current tag/bookmark icon is pretty confusing). In general the more users can use org files, the more text they will have and the more they will need search, so there is a pretty good feedback loop towards upgrades.
Some thoughts on the search UI itself.
I think the current TODO screen has too many different options on it that are kinda confusing: "Everything", "Incomplete Tasks", "Show All", and the picker for different searches/filtering. I think I understand all of these now, but they are pretty confusing and they really take up a lot of screen space. Some of these naturally would fit as their own filters onto the main search listings I described above ("Show All" certainly would). The others I think would work well as options on particular searches. Currently each "saved search" is only a search string. I think a search should be thought of as more than that. It should also include the sorting that should get applied, options such as whether to match everything or just headlines, grouping by files or not, etc. This way when a user clicks into a saved search, they will be able to see both the items that they want, and in the order that they want.
Saving a search should be a bit more prominent also. Maybe a full "Save" button (also a good call to action to trigger upgrades). If it has already been saved, then that button is where the name can be displayed.
Anyways, thanks for all your work, hope the ideas in here are helpful.
Thank you for your detailed thoughts on the search UI. I definitely agree with most of these. My personal use of the TODO tab is as an entry point to various saved searches - for example what are my in progress tasks - so a refocus of the second tab is something I want to look at. I shall take a more detailed look at this when I come back from my holiday starting this week.