I have the impression that the CC people actually DO listen to their customers. I know positively that they are working on an update for SD3.5, because I have seen a Beta version of it.
Their first priority, after having launched a major update, will of course be to make sure that everything is working as intended. We discovered a series of flaws with v 3.5, so that is what they are fixing at the moment, but they are also adding more features. When it comes to what features are being added, your guess is as good as mine, so we'll have to wait and see. At any rate, adding a feature is typically not something they can do in just 5 minutes.
As to the building blocks that you find on the Bootstrap and Foundation websites, yes, some of them are a bit tricky, because you need code which has not yet been added to SD (e.g. things like ::before and ::after, off the top of my head). But it can all be done by using external css files, or adding it to the head section in Page manager. If I can manage it, someone else will be able to do it too. It's actually just a matter of 'boldly go...'
But of course, it would be nice if there was something similar to the Materialize theme and building blocks, also for Bootstrap and Foundation.