I'm also interested in this topic of a computerized index card file.
My intended use would be for storing and cross-referencing data items in research programmes. Like many researchers I have missed logical connections between related facts - and sometimes this resulted in not pursuing more productive lines of enquiry.
Doing my research in 1990s I saw others making entries to a physical index card file. But I never saw anyone using their index file to suggest new directions for their research. (This of course may have been done secretely or out of the office.) It happened once then that I missed applying some phenomenon I had read about in a paper when examining an image. The effect of the phenomenon was noticed but I explained it as due to some other (incorrect) cause. That made me question my own purely mental way of connecting facts. A more striking example occurred years after completing a project when I rationally connected about 6 core facts in the old research topic and found an astonishing and counterintuitive conclusion.
Today, a database allows us to query multiple cross-references between items in different tables. We may add new keywords to our record index as our programme continues.
I believe in research towards worthy objectives. These objectives may be very specific, e.g. a quieter lawnmower, or quite general, e.g. exploring a new phenomenon so as to characterize it and its limits. But research budgets in every country are limited and none of us can really afford to be attempting things that are impossible or very unlikely. An online or standalone logical query system is something that could provide useful savings in research programmes as well as speedier advances in technology.