There are very similar test strips mounted in cassettes for detecting all kinds of things. I think I've seen them for detecting food poisoning or allergens, various pesticides, pregnancy, ovulation, colon cancer, etc. Even COVID-19 now:
https://www.surescreen.com/products/covid-19-coronavirus-rapid-test-cassetteThey can be used "manually", but as you say most just need a simple image sensor of some kind to detect whether bars appear in the appropriate places for a valid positive or negative reading. A mini spectrometer can be also added but still adds a fair bit to the cost, although far less than it used to. You just need a barcode reader to read the barcode or QR code on the cassette which encodes detection type and expiry date, and you can make a reasonably low cost and widely useful rapid diagnostic device.
Similar machines already exist for certain testing industries, just not for consumers. I've actually consulted on building such a machine. Once you design a sexy enclosure, add electronics & touch screen, software for UI and "image" processing, test and calibration procedures, build marketing, support, and distribution channels... you suddenly have a product that costs many thousands of dollars each. A long way from where we started with a single use pregnancy test for a few bucks.
It is actually incredible that these disposable pregnancy tests can include the electronics and still be so cheap. It just happens to be a market that has the sales volume and people willing to spend a few dollars more for a "premium" product.