Residential is far different from commercial. I've covered a range from 1,500 to more than 18,000 on residential. The only commercial I will work on with an architect is light commercial, but I prefer staying residential.
I work with Softplan, so slightly different than how it works in comparison to Autocad. It's closer to Revit as far as drawing style. But the good thing about Softplan is the file size. Since it actually splits each floor into a separate file, it helps keep it down. I typically don't go above at most 500k per floor and that's a big project.
The app I am talking about would be very simple. Be able to draw a wall width at a time rather than individual lines, so pick your wall width and have it treated as rectangles. Then door and window symbols. And dimension them. That's all. I don't care about notating and bringing up elevations, that's what the desktop is for. This would be simply for doing a quick and dirty floor paln entry as built or conceptual and then either export as DWG, DXF or DWF, even Adobe would be fine, into my regular desktop computer, to clean.
The kicker is, this kind of application would be useful to architects, designers, builders, remodelers, insurance agents, fire and disaster companies, even county governmental agencies. The base is huge. I just don't have the connections to get a developer that could work on this without costing an arm and a leg. I've been talking to Softplan about developing it but talks are slow on that one. But like I said, compared to the CAD apps out there now, this is not only doable, it would be VERY doable on the iPad and would be an outstanding tool.