Is there some way to edit the text of an index card in one editor window while the corkboard or outliner is in the other editor window?
What is your setup, and what trouble are you having? I selected a stack of documents in the binder, and then selected the cork board view. I then split the view, so that there were two identical cork boards. Then I edited the synopsis of one card, and hit tab to complete the editing of that card. A second or two later, the edited synopsis appeared in the other cork board.
Are you having some issue with this scenario?
When you say “edited the synopsis of one card” do you mean you clicked in the card to focus on it, double-clicked in the card to make it editable with all text selected and then clicked again to deselect all the text and set the insertion point? 4 clicks! That’s crazy. I see why it’s happening but I doubt all those steps are necessary.
I’m not using that scenario.
What I want is to have either the corkboard or the outliner in the top editor and then edit a single index card or scene synopsis text in the bottom editor. And also simply click on another card or outliner row to edit that synopsis text.
Currently I see 3 ways to edit synopsis text: corkboard index card, outliner synopsis field (if showing) and index card in the Inspector. Corkboard takes 4 clicks to make the index card editable. Outliner takes 3 clicks to make the index card editable. Inspector takes 2 clicks, 1 to pick the card and 1 to set the insertion point (which is only 1 pixel wide). Both the Corkboard and Outliner have issues with vertical scrolling with the mouse wheel since the text can scroll and the window can scroll and you can scroll right out of the editor. All this makes for goofy operation and makes both Corkboard and Outliner best used as ‘views’ not editors. They’re both really good as views. I simply want to use an existing text editor window to edit the synopsis text.
I think I’m missing something, but from a pure click efficiency standpoint, how is editing the card in the Inspector any different than hypothetically editing it in the text editor area? There is no way to do the latter by the way, and probably never will be as that would confuse the role of the editor, and seems a bit superfluous to me when the inspector pane can be sitting right there offering easy one click editing at any time.
So yeah, two clicks to edit the card in the inspector. I really don’t see how that can be optimised any further. You can’t eliminate selecting the index card. You’re going to have to, at some point, give the software a hint as to what you want to do. So that’s always going to be there. And then you’ve got to somehow tell the software why you’ve selected that item. Selecting it is a passive event. Clicking in the synopsis card in the inspector is a more active event. It can’t guess that this what you wanted to do. You might have wanted to go on and pick three other cards in the corkboard, and then you would find its insistence at focusing the card in the inspector to be quite annoying as all you were trying to do was keyboard arrow through the cards and read their document notes (hypothetical situation).
The only way I really see room for improvement here is adding keyboard access—which we will do. Practically every component of the interface window will have a keyboard shortcut so you can jump to it from wherever. Maybe you press down-arrow in the Binder to select the next piece of outline, then hit SomethingSomethingKey and now you are typing in the synopsis card. That sort of thing—it’s really no more or less efficient than clicking though, it’s still an action just a different type of action.
This isn’t about clicks or navigation. I would gladly click 5 times if my synopsis would appear in a fully featured editor. I would really like to do things to the synopsis like bold and highlight colors. Notes allows that; why not synopsis? It appears that allowing synopsis text to be in rtf files is what needs to happen. So do that. Make it optional or whatever it takes. Just don’t restrict me.
One benefit of full editing synopsis text is this: sub-scene status.
Scrivener covers the chapter and scene status well with First Draft, etc. but it does not address sub-scene status. By sub-scene status I refer to something within a scene that I discover needs attention but maybe not right now. So I select a sentence or phrase in the synopsis and highlight it. Maybe I use 3 colors to indicate priority. This is then clearly visible in the corkboard or outliner. It won’t be forgotten.
Note: All questions are rhetorical.
Since the questions were rhetorical, this isn’t meant to answer them, but just to voice into the wilds a suggested method which may provide some of the visual cues sought. 
Since synopses are by current necessity plain-text, using a series of asterisks or similar symbol to indicate levels of priority (as you might do with a highlight) could be a way of marking up sections to indicate importance:
Blah blah blah blah happens.
- He’s wearing a yellow shirt
!! Plant the murder weapon here
Another idea is to use the document notes (rich-text) to indicate the specifics of what you want to address in a given scene, since this also allows more room to get into detail of ideas, what needs changing, etc. as well as allowing highlights and so on. You could then use a keyword or a few keywords to indicate a general “needs addressing” or such which you can drop on your index cards; if you have the corkboard options set to display the keyword chips, you’d then still get the visual indicator there of scenes that have items you still need to address, and you can then funnel down to get more specifics. You could also use the keywords to create dynamic collections of scenes that need further work in specific areas, etc. which might be convenient as well.