Improvements to endpoint path UI field
It should be possible to edit the text of the endpoint URL always, even after selecting an endpoint from the list. Currently the only way to do this is to click the X button to the right.
In the old version of the console this is possible by pressing backspace inside either of the two text fields at the end of each endpoint:

This is a little better, but still kind of annoying: I would like to be able to click anywhere inside the endpoint URL and edit it.
IMO, this may not be a good idea. Can you tell why do you want to do that?
But anyway, this may be a little complicated to achieve :P
Yes, this is my # 1 biggest frustration with both versions of the API console:

It should be very easy to switch between different URLs for different endpoints. Let's say I am looking at /posts, then probably I want to go to /posts/:id next. I should be able to do this by quickly editing the existing URL, rather than having to find the x button all the way at the right of the screen and click that.
We should be able to edit every part of the URL at all times. This part is pretty easy, right? What is maybe not so easy is managing the connection between the currently selected endpoint and the available parameters. What other complications can you think of?
IMO this is a major usability issue that we need to solve anyway.
When we are done here, maybe we still have the x button on the right, but I should never have to use it unless I really want to clear everything about the current request.
Also, the HTTP method is similarly "locked in place" after we have selected an endpoint - POST is another valid method for /posts, but probably I should still be able to choose any method:

Oh I see! SO if I understand correctly, the thing to do is,
1- When editing the URL, try to find the corresponding endpoint (filtering the endpoints list correctly). But I think we should reset the selected endpoint on the Redux state, that would have the effect of clearing the Query/Body param builders. I think it's ok since the params are still on the state so the next time we match/select a new endpoint, they will be back (and still filled).
I think the most difficult part here, is to update the filtering to be able to filter the endpoints ignoring placeholders.
2- When editing the method, match the corresponding endpoint and select or unselect the endpoint if none matches.
Your 1- and 2- sound reasonable to me.
I think the most difficult part here, is to update the filtering to be able to filter the endpoints ignoring placeholders.
For the v2 API, we already have a regex that does exactly this. For the v1 API we will have to build one for each endpoint.
Maybe once you start editing the URL you just get the list of endpoints that could be potential matches, and if the currently selected endpoint is no longer a match then the param builders go away (with params saved in state) until you select another endpoint.
I agree that having the filters and params work correctly with any user input is the tricky part. As long as they still work when you select an endpoint from the list, I think that will be good enough.
@youknowriad - I'm removing this from the "WP.com launch" milestone. I still want to do it, but it's not in the current console and it will need lots more testing to get it right.