Having said that, I use a Billingham F2.8 for my Panasonic GX1 a couple of kit lenses and a flashgun. It's far from a custom fit but I find the additional space useful. One other drawback, Billingham's are expensive in the UK and very expensive everywhere else.
Try a search on DPReview for camera bags on the Micro 4/3rds forum. That will give you some other suggestions (Domke, Lowepro etc...) and a better idea of what others are using.
The bottom line is that you're unlikely to find one bag that's perfect, especially as you may find your camera system grows over the years.