I think it would be a nice feature that will allow to create topics without the restriction to have to choose a category at first. The Tags are enough for categorizing stuff. And some may want to have their forums without categories. Just topics.

Hi

That is something very difficult to achieve since topics are tightly integrated with categories

But, we can definitely do something like this:
Create a category named "Uncategorized" and make it the default category when none is selected.