The problem is I don't think every answer needs a mini-app. I'd argue there are very few answers that do. For example, it feels like Google's featured snippet (quick answer box) but expanded. But the thing is, many people don't like the feature snippet, and there's a reason it doesn't appear for many queries - it doesn't contribute meaningfully to those. This functionality is doing exactly the opposite of the process…
I tend to agree: I don’t understand what the “one-off app” is trying to achieve. In the example of the rental apartment—the user specified the parameters in the query. Just apply them, right? I offer this in the spirit of feeling like I’m missing something, not out of negativity—I just genuinely don't understand the proposition. What’s the advantage of trying to extract and normalize features from already-messy data…
Many years ago in college I worked on building Java applets that let kids visualize math related concepts. Sliders make things like sine/cosine and all sorts of other cool stuff way way more intuitive. We had a applet that, let you do ridiculous comparisons, to visualize how many empire state buildings a marathon is in length, etc. We had an primitive 'engine' simulator that let you adjust inputs on a steam engine. stuff like that