Bodhisattwa Mandal, 29/07/20 00:40:
Coming from a community with not much volunteer force, I actually want any strategy which involves minimal human interference into the tagging process, as we can't afford to spread our thin line.
Anything that goes into the wikitext has an implicit cost for humans. Already the templates we use for mere formatting and layout make it costly to do relatively simple things such as "give me a plain text version of the book", although they sometimes manage to make other things easier (such as making a decent HTML version which may also work in EPUB).
If the purpose of linking "persons, places, creative works, events" to Wikidata is to provide marginally faster information to the average reader browsing the Wikisource website, then you can do it with a JavaScript gadget similar to the various Wiktionary gadgets which we've had for a while, and take a probabilistic approach. If the purpose is *disambiguation* (and attendant features like structured search), then it's quite a different matter.
We probably can't afford an approach like METS/ALTO for any significant number of works. Nowadays people do all sorts of fancy things with IIIF but I'm not sure about detailed tagging at scale. The advantage of something like an IIIF manifest is that you can store it separately from whatever we have now, and "just" overlay it on the images (merging with the wikitext and HTML is going to be harder; compare efforts by Alex_brollo with hOCR/DjVu transfers).
You can probably imagine a relatively simple gadget to suggest possible Wikidata items to connect to some parts of an image and let the user confirm or not with a single click, then store the result in a JSON on a wiki page. If it's designed for the Page namespace, maybe it can even be enabled by default on a willing subdomain without disturbing casual users. If some focus is determined (say, "depicts"-like statements for illustrations in books), it might be possible to have some perceptible progress with an edit drive à la Wikisource birthday prize, to attract new users beyond the usual suspects and generate some enthusiasm.
Federico