You can suggest whatever you want, I will see it and might reply (It might even be added in the full game)
the one you have played is the prototype
Possibly add some use to all the coins and boxes you receive for satisfying customers? like being able to open the boxes for more materials (eg random item or crafting material) and maybe a store button, where you can go to a store and spend your coins on more metal, more wood, upgrades, etc.
Obviously some proper menus would be good. Some kind of anvil system to add a little more complexity to the crafting process would be nice. I'm not entirely sure how best you could implement player agency in what type of shape you get out of it, but it would be nice to allow players to craft the wrong thing by accident. Maybe something as simple as hammering the heated metal a different number of times depending on the product you need. Eg, hammer it once, cool it off and you get a hammer head. Hammer it twice and cool it off, you get a spearhead, three times it's a sword blade etc. Making customers get impatient after waiting too long would be good too, adds a bit more challenge to things.
Effectively I'm thinking it would be cool to have it working similar-ish to "Cook, Serve, Delicious!", but 3D, and crafting medieval weaponry instead of food. :P Of course what you do with the game ultimately is up to you, but this is a suggestion thread after all!
A shelf-system where you can store all the materials. Right now, everything is just flying around and trying to organize it manually... Yeah, good luck. Either something where the materials just snap into place, or a system where the shelfs appear a bit filled with the specific material, and you can click on it to get / store material.
More recipes, and maybe unlocks after a while.