belles-lettres or diplomatic provisioning

As much as penmanship is a vanishing art, so too is the is legible and literate eye for penetrating not necessarily historic documents of great importance and concern—as the discipline of diplomatics mostly concerns itself with, but also for the everyday that’s receding out of our scope of what’s readable.
Like how I’ve heard that parents can use cursive as secret hieroglyphic code (like spelling out matters that aren’t meant for sensitive ears), we can’t train our gaze to the compact and economic handwriting that fills up older postcards and other correspondence when paper was more a premium commodity, rather than just an unpolished draft and cue to toss away. A diplomatic transcription is a faithful reproduction of a manuscript with no effort to bring it in line with modern conventions of modern copybooks. I suppose such calligraphy will never be wholly unbroachable to us in the future—thanks to advanced optical recognition, but I do wonder about the fate of collected letters and other non-ephemera. What do you think?