Fair enough, though I disagree with these points. For one thing, this feature already works, so I don’t expect it will take any significant amount of time from the LessWrong dev team.
But to respond to your more specific points, from my perspective:
(1) there is a common misconception that flashcards and/or spaced repetition is mainly useful for facts and definitions. It is also very useful for concepts (“a generative adversarial network is...”), takeaways (e.g., “the most important three points this post makes are...”), connections between ideas (“X and Y are thought to be different but they are connected through Z...”), strategies (“Here’s a process you can use...”), and so on. I certainly don’t think all LessWrong posts are suitable for this, but I think you’re underestimating how many are. My guess is it is a good fit for 5%-20% of posts but that’s a super rough estimate. I personally use flashcards for complex concepts all the time, including plenty I’ve created for myself from LessWrong and Slatestar Codex posts.
(2) indeed it is a standard belief that if you pick up someone’s random flashcard deck that they wrote for themself you are unlikely to get much out of it (I agree with this too). That is different from a deck written specifically by the author for an essay (almost nobody has experience with this, other than through the experiments I link to in the bottom of the post) so the “I can’t pick up my friend’s deck” argument doesn’t have much weight in this case in my view.
(3) I would argue that even posts that e.g., “work towards reducing confusion about things we are currently confused about” have takeaways that are worth remembering (e..g, “what should you think about differently having read the post?”, “what was the approach of reducing the confusion?”, “what is a useful analogy for thinking about this topic?”, etc.)
These are all quite reasonable, and I’m pretty open to the idea that I’m mistaken and anchoring too much on the fact that I didn’t find flash cards for spaced repetition useful, which might ultimately bias how heavily I weight things or assess the likelihood that flashcards would be helpful.