I'm just guessing at what you all might find interesting. They're informed guesses, but guesses still.
In this case, these guys are working on something big and the background from which they're approaching the problem seems solid to me.
There's an interesting delta here between how YC thinks about startups and how HN thinks about startups. I'll try to come back and add more to this comment because it's something I've been meaning to write about for a long time.
Edit: here it is...
Think of the current state of a product like this as a point on a plane. When YC funds a startup, they're not so much looking at that point, but rather at the vector it's part of. That includes, yes, current position, but also direction (how it might develop over time) and momentum (how fast it's developing, how capable the founders seem).
When HN evaluates a startup, people really just look at the current product point: how valuable it is right now, i.e. how ready to fill important use cases and how good a business those make for. That's a perfectly fine thing to assess, but it's a totally different assessment. This is the delta that I mentioned above.
Partly this is because of a difference in the amount of information available (YC gets detailed applications, gets to interview founders, works closely with founders during a batch, and so on—HN posts don't provide any of that). But partly also it's a difference in mentality. YC is making decisions from a place of high uncertainty. HN, or at least the critical side of HN, only values what can be demonstrated today and has low tolerance for uncertainty.
For YC, the home runs are funding a company that starts out looking like a toy and ends up developing into a big business. But if the startup does a Launch HN while still at the "toy" stage, HN tends to have a big allergic reaction: "how could YC fund such a thing?", etc. etc. Well, YC is funding such things all the time. That's the core of the business. A few go on to get big and then the startup (or YC) gets to point back at threads like this and say "I told you so". More, of course, never amount to much, and in those cases it's the commenters who get to point back at threads like this and say "I told you so". It's hindsight fallacy in both cases though.
The lesson for Launch HNs might be that it's in a startup's interest not to come to HN while still at the tadpole stage, when people say things like "I can't see how anything productive or useful could have possibly come about from this thread". On the other hand: those are just comments, and only part of the comments at that. There are also bound to be a lot of users who are interested in the vision and willing to try the new thing even if it's in an immature state. So it's actually not so easy to say what's in the startup's best interest.
It's much easier to say what's in HN's best interest: interesting conversation. I'd say we got that here. Alternative/future web browsers are an interesting theme, and while the reception has been mixed, I wouldn't call it a flamewar. It was a bit unpleasant at the negative end, but then other commenters have shown up to compensate for that. That is the natural cycle of many HN threads (https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...).