To me it sounds like there are three points of view here:
WW: Developers should never wrap params, dirty root is fine, prefer to deprecate the wrap_parameters feature (rebutted by DHH below)
DHH: Wrap parameters is useful to normalize between the common JSON style of not using a root and the common CGI style of using a root.
JFB: People should always write their JSON to use a root per an emerging standard. (Possibly with the corollary that if everybody does it this way, you don’t need to wrap parameters anymore and could then either change the default of wrap_parameters or deprecate it?)
In my experience, the current behavior of wrap parameters works well for the reason DHH mentioned, in addition to automatically normalizing rootless JSON with XML posts, if you need to support XML (rootless XML documents not being a thing).
Anti- or not, a lot of client side libraries prefer the no-root-in-the-JSON pattern at the moment, so I feel like it’d be pretty early to move in that direction by changing the default of wrap_parameters to false, if that was the implication of Jason’s post. I would love for there to be a consensus on root nodes in JSON, but at this point the deploy base of non-rooted JSON is probably vastly larger than rooted JSON (I have no statistics on this, just a sense from third party JSON APIs I’ve been consuming lately). The fact that it is configurable but leans toward supporting non-rooted JSON seems like the right answer to me, for now.