Kind 1 with a k Tag or a generic comment kind are both "final implementations" (you rebuild it once and you're done). Seems neater than plan Kind 1s, at least.
Discussion
even kind 1 with a "k" tag wouldn't fix the issue of social clients having to filter out every reply just to show a timeline
a generic comment kind would be a clean solution since it would not show up in the social timeline and would allow clients to show just the replies
however NIP-22 might need to include "p" tags for notifications
I'd argue a generic comment kind would be well-served by AsciiDoc support, as it opens up more rich text options and makes the kind 1111 events appealing in a broader range of use cases.