@garius I don't know what Twitter does, which is why I'm asking :-)
I suspect you know this already, but it might be worth saying ...
I can include an explicit link to your post, and it's up to your client to decide what so do with it. The UI for doing this is different from "reply" and isn't obvious.
Plain Mastodon behaves differently from forks like Hometown, Glitchsoc and so on. It also renders differently from the various app clients for Mastodon, and of course is different again from the many non-Mastodon fediverse services like Pleroma, Akkoma and oh so many others.
Some of these will already have the "QT" functionality that you want.
But I suspect that isn't enough, you aren't actually asking for you to have this UI option, are you? That's not going to help creators, they're not going to benefit by QTing their own posts anyway. You're asking for everyone else to have this UI by default, I think.
I'm not sure I've completely understood why a simple Reply to a post saying "this is cool" isn't visible enough. Here, I might be misunderstanding Mastodon myself ... I often see middle-of-conversation replies in my feed, from people that I follow, and if they look interesting it seems easy enough to click on the thread and see what it is.
But I do think you're only really looking for a different UI gloss over the features that are already present.
https://mastodon.me.uk/@garius/110159790530289077