The UFAQs on NRDB are also very nice, I think they’re a good move.
In an ideal world, of course, the official FFG card database would handle rulings nicely. But it’s completely useless for rules stuff. It doesn’t even list errata, despite being the source judges are supposed to use if they provide card text during a tournament.
But yeah, Slack is not a good place for rulings. They disappear after 10,000 messages, and viewing older posts is hard even before they disappear, and of course there are people who don’t want to join Slack who still need to be able to see rulings. It’s fine that rules discussions on Slack lead to rulings, of course, but if they’re rulings that are likely to be needed outside of the specific discussion in which they occur, they really need to be copied or repeated somewhere else.