Adding sandbox elements to a kinetic VN after you already have an established fan base. Is probably a horrible idea. There are a lot of us that just want to sit back, relax and enjoy a good story. Without having to click around a bunch. Worry if you missed something, and feeling like you have to look for a guide.
Even if it's just small stuff like letting you free roam around the house now and then. It could rly break the immersion for allot of ppl.
But anyway. It's cosy's creative vision. And I respect that wholeheartedly. And since there were no sandbox elements at the start. I suspect that it was never in the plans to begin with. Could be wrong though