I didn't buy mine for a pack, I bought it for ground hunting turkey and deer. It's perfect for this because of its light weight, comfort, and mobility. There is no problem carrying the average day pack on it as it is.
I haven't had a need to modify mine any, but the way it's constructed, it would be simple to fit just about any belt/shoulder system on it. There's no problem drilling additional holes in the frame if need be for any attachments. I'm sure it would have its carrying comfort limits, but I'm also sure it would be a capable substitute.