As a kludge, and certainly not an elegant solution, but for now you could start the rule name with your category and the alpha sort would give you that effect.
Grouping/nesting of rules has been a feature request for some time. It doesn't seem to be getting much love unfortunately - I'm not sure why. I prepend rules with 'Lights - ', 'Notification - ', 'Curtains - ' etc depending on the rule content. The long list is still annoying to navigate. The easiest way is just to type in the search box what you're looking for to instantly filter your list; I'd missed that feature but find it very handy after someone mentioned it on here a week or two ago.