Handwriting definitely helps, but a lot of it in this system is done during reading (or just general life), which Ahrens calls "literature notes". Ahrens has a theory that handwriting forces paraphrasing, which he views as important to learning. Anyway, I handwrite all that, then there's a later stage of integrating the relevant info into the system.
For me, searchability and accessibility, plus backup (I write a ton on paper already and I'm a bit worried about losing notebooks) makes it worth the digital step.
Also, I suspect from initial usage that the Zettelkasten is what Krakauer calls a "complementary cognitive artifact": https://philosophicaldisquisitions.blogspot.com/2016/09/comp...
I.e., it makes you better at what you're trying to do even in the absence of the tool. To me, the main benefit of the system is that it encourages relational thinking.
Regarding handwriting, I'm of a similar mind, having evolved my own system (hybrid of bullet journal + "slice-planner" in monthly moleskine quad-ruled paper journals, plus .md files and evernote) which is in need of some refinement.
Stylus is indeed big step in this direction, but still is a tick off. Also with a tablet you tend to suffer from "modern technology"-syndrom, meaning you wanna utilize all the good features now that you have it at your stylus tip. But they tend to make thinks complicate aagin.
I have seen many good and useful apps come and go. After these apps become abandonware[^1] we have tons of data created in those proprietary data formats, trapped in them.
[^1] off the top of my head: WordPerfect, MS Word pre 2000, AskSam (fulltext database), Netmanage‘s ECCOPro (a PIM), NoteMap (an outliner), MindJet‘s MindManager, MS Access pre 2000. - Tons of data that I created in those apps waiting to be migrated.
I wonder, though... I think writing something by hand gives a different feel for it. I don't know how to explain it. It's like your mind works better if you write by hand.
So maybe an app, used with a stylus on a tablet or large-ish phone might be the best combination? It should then create folders and textfiles, and just store the text there. Which would require OCR and proofreading, of course. But that shouldn't be an issue.