Technically, yes. Practically, Leaflet seems OK with it. There might be some inefficiency in having Leaflet interpret the strings rather than the native JSON parser. But we also shouldn't rely on that. The TopoJSON converter choked, for example.

I vaguely remember that we had a motivation for using a form encoding instead of JSON, but I don't remember what it was. Since we don't have cross origin issues (and don't support IE < 10 for mobile anyways), there shouldn't be a problem with posting JSON.

Anyways, just wanted to add the note, so if we do any work on that code, we can take advantage of the opportunity to fix it.