My guess is that if the skin was going to remodel to not be loose it would happen while you are losing the weight. I cannot see any plausible mechanism that would make the subcutaneous fat containing tissue, and the stretched connective tissue fibers that support it and give it it's structure, return to the original state. Some body parts definitely remodel over time in response to stresses, bone getting stronger with stress from exercise for example, but there are no active forces compressing that tissue to try to force it back into shape, and no biological processes occurring in that tissue that would make that tissue underneath the skin contract and tighten up the skin. The loss of tissue volume from fat loss while losing weight would provide a little bit of negative pressure, but this would stop as soon as weight stabilised. Injecting compounds causing subcutaneous scarring and contraction could conceivably do this, and I would be surprised if no one was selling this process, but is very likely to lead to lumpy irregular contraction that would look worse.
Compounds like KLOW and GLOW etc are advertised to increase subcutaneous collagen production, but not scientifically tested in humans. If they were effective enough to do this on such a scale as to meaningfully help this problem, I would be terrified of their effects in promoting cancer and tissue fibrosis in other body areas.
