My idea is that there could be a new furnace added to the game. It would be called the Redstone Furnace. The Redstone Furnace would be crafted In a recipe similar to a regular Furnace. This is how it would be crafted.
The difference between a regular Furnace and a Redstone Furnace is that it is 50% faster than a regular Furnace. To get a Redstone Furnace to work, You must have a redstone signal going to the Redstone Furnace, that could be a lever, a repeater, redstone, etc. Depending on how many signals you have going to it, that determines how fast is cooks/smelts. If you have a lever on all 4 sides and the bottom, your Redstone Furnace will be 50% faster. If you only have 1 lever, it will be 10% faster. Also, the Redstone Furnace still require coal, but coal is more efficient, if you use the Redstone Furnace with a redstone signal connected to it, coal will have 12 uses instead of 8. You dont need to have a Redstone Signal either to use it, but it will be less efficient on coal and will be the normal speed of a furnace.
I actually have an idea, to make it more original. What if, it did require redstone to go, but it when it was cooking something (like meat or ore), it would act kind of like a repeater. In that, I mean, it would send out a redstone signal, that would be full strength. I think that would be cool for maps.
What the, if the furnance won't consume any redstone in it's process of cooking/smelting, then it means you have made the original furnance obsoleted. And its child's play to make a furnace of your blueprint, so it will absolutely unbalancing the game.
Redundant: the key to cooking fast(er) is to use multiple furnaces at the same time.
In my eyes this isn't really necessary, for I can cook enough meat in one day for the next six days, and smelt enough for an entire armour piece in relatively good time as is... But it's not like I'm some mass producing factory, so...