It's basically self-explanatory. I would love to be able to detect how full a large tank via redstone signal. It would allow for some fun automation trying to optimise certain processes, for example trying to keep the LSB at max temp until the tank is full, making it more coal-optimal if the player is willing to build a little circuit to control it.

I think it would make the most sense for the signal to come from the hatch, though this does make me wonder if something like a redstone hatch that could be generalised to more machines would be a better idea.

yes, please!