It would be difficult to do properly, unless it just cached only what you were looking at.
Most links in HN are to external sites, so you wouldn't want to be caching them on your phone. Then there's the amount of traffic to HN meaning that you would be caching massive amounts of data only to get mostly unusable links, and some comments about them.
I agree that it would be nice to keep reading things after you go offline, but I think the technical side of it would be prohibitive.
I agree, a "good" solution to this is hard. But I'd rather have a very bad solution right now, and if someone comes along and iteratively improves it, so much the better. Something like the text of the top 30 links + the ones you were reading in the last hour. A refresh button that updates the current content if it is changed, and an update cache to update this cache. I will certainly be very happy with something to start with.
Most links in HN are to external sites, so you wouldn't want to be caching them on your phone. Then there's the amount of traffic to HN meaning that you would be caching massive amounts of data only to get mostly unusable links, and some comments about them.
I agree that it would be nice to keep reading things after you go offline, but I think the technical side of it would be prohibitive.