Let's see. Just thinking out loud ...
What's the purpose of a category? Why have any at all?
What's the cost of having separate categories? Among the costs:
It takes longer to ask a question.
It crowds all the categories if you have too many.
Questions that were put in the wrong category (at least 20-30%) have to be recategorized.
Someone browsing one category won't see questions in another category.
Among the benefits:
If you're interested in one category, but not another, you can just see the questions you're interested in.
Are there other benefits?
Do the benefits of subdividing a category like "WikiTree Tech" overcome the costs? For me personally, I'm going to have to look at all the questions in WikiTree Tech, whether they're questions or suggestions, so I'd rather have them together. Plus, I think a question often leads to a suggestion, or vice-versa, so it can be hard to separate them.
Speaking of which, Lindsay, you asked a question inside your suggestion: Can questions be in two categories? No, unfortunately not.
Back to whether questions and suggestions should be separated. Like I said, for me, personally, I'd rather have them together for convenience. Are you saying you'd prefer to have them separated so that you only have to browse suggestions? Or maybe you're thinking of the people who have questions. I don't think people looking for answers to questions generally browse the category first. They'll just ask or search (and the asking auto-searches).