Yeah, slide outs sound nice. There's some video's on youtube about people putting in slide outs that appear to be way under engineered. I don't know how they're built in an RV, as in photos of RV crashes you usually can't identify the slide out.
I like the idea of the extra space, but at the same time the reason I chose a bus is because of how safely they're built structurally. I don't want to cut out support structure to add some extra space.
I subscribe to the KISS theory. I resist the urge to drill any holes in the roof and I keep my furnishings simple. I've got a medium size bus which allows me enough space to have a garage in the back of the bus.
As always, each to his own. I'd enjoy seeing a slide out built and set up. I'm sure I don't know how to do that. I'd want a coach to do that kind of work on.