Design Ideas in a custom theme

I agree with you. To clarify, some of this you can already do in PowerPoint by customizing slide masters and saving the presentation as a template. You can even add multiple top-level masters, which become alternative "designs" in the gallery when the theme is applied. So, some of that is already supported.

But I think you might be suggesting that we should be able to further customize templates, and I think that's a great idea. Specifically, I'd like to see PowerPoint give users the ability to create:

• Custom animations and transitions. There should be a system whereby you can create or add canned animation and slide transition effects beyond those included with the program. Perhaps these could even be available via the store. I realize that quality animations are sophisticated and probably required a fair amount of precision and programming, but it would be a welcome addition to be able to expand or even just combine the core animations and transitions for reuse.
• Repository. You should be able to create and store complex groups of shapes and sequences for reuse. For example, I have a lower-third graphic that I like to use to introduce a speaker, but aside from copying it from one slide to another, there's no good way to make it reusable (and no, masters don't work this way, because any objects on the master appear behind the slide contents).
• Styles. All the other Office applications have styles. So why not PowerPoint? You should at least be able to use built-in styles similar to Word, Excel, or OneNote. But you should also be able to create custom styles. It would promote much more consistent and professional slide designs.

This is a great forum to discuss ideas, but PowerPoint has a UserVoice page where you can actively submit and upvote this stuff. Maybe somebody will listen!