I know that an option exists to auto-generate a synopsis from selected text, but I find myself wishing for another auto function. It would be cool if the synopsis could be auto generated using the first sentence from each paragraph in the document. That way, I could easily check the flow of arguments, logic, or generally just the overall flow. This is really only of benefit for those doing expository writing, but if you follow the practice of putting topic sentences first in your paragraph, then it would be easy to check your flow using the corkboard.
This notion has been discussed before, and while it does make great sense on the surface, there is a more subtle implication that can cause problems. For a long time we had to tweak the UI to get people out of the notion that the index cards are the manuscript. It was a long-standing problem that took years to fix. At this point in time, this sort of confusion has kind of dropped off of the radar entirely. It is now easier to understand how the interface works; how the index card has nothing to do with the content except to serve as a reminder of it.
So, with that history in mind, the problem with your suggestion is that while it would be a great convenience to people working the way you do, it would also serve to further the notion that what is on the card is the content. We’d have people making edits to the prose on the card, and then only much later realising all of their edits never made it into the manuscript because they edited the card (and unhinging it from automatic updates) and not the content.
That is the danger with features like this. Even if you make it a preference, people will find it and turn it on not really understanding the implications. We had problems with people compiling empty documents because of this, they were writing their whole book into index cards.
So we’ve actually done more to reduce automatic proliferation of data into the index card, and I believe that has gone a long way toward reinforcing the concept that this isn’t the document. Making the controls manual, something you have to do yourself, has made the divide concrete. This is the reasoning behind the current design as you use it.
Flipping this around, have you tried breaking your documents down to the paragraph level? Index cards could then be more specific, just holding that topic sentence, which might let you use them to greater advantage in structuring your document.
Yes, I had considered this, but I found that this reduced the document almost—and I’m not trying to be rude here—to a nonsensical level. I think that the document works best when it contains an idea, which ideally should take around 3 paragraphs to introduce, explain, and summarise.