@blakehensley@washingtonpost QPs are on the roadmap for Mastodon https://joinmastodon.org/roadmap. As for why some clients support a qp-like feature, it's a popular requested feature and not difficult (imo) in practice to provide. A QP is really just a link to another post where you can see the text and OP account. I think whether it works or not in other clients will vary.