Longline bra or corset?

I finished the 3rd mock up today, and as I did the fitting I noticed that the fabric wrinkles a bit in the back, and the sides as well so I think I'll have to add boning along some of the seams. I'll also make it longer in front so it extends further down, cupping the tummy, and increase the height in the back. This will end up a corset with cups I suspect. I suppose I could make it front closing as well, and use one of my old busks, but that would stiffen the front considerably.

I've never made a wearable mock up before, but perhaps the time has arrived for it to be a sensible thing to do. Thing is at the moment I don't have any powernet fabric. I've ordered it, but it will probably be a week before it arrives, so if I'm to make a wearable mock up I'll have to find another solution. Perhaps cut up a pair of control top tights, or use double layer merino wool jersey. Or I could stitch together wide elastic to form panels.