I'm assuming that the OP [...]
Did you just assume OP's needs?
I have a different opinion. You can get decent renders in 1-2 days by following video tutorials. Learning is not easy, but it is fast. Fast and painful. Steep learning curve gets you exactly that.
Regardless, getting a tool like you describe is quite possible. Not a web service, but you could get it via addon for Blender (or 3dsmax, or maya, or modo, or whatever, but Blender is free, has built in renderer, and is not much different in the end). You just need to automate some tasks normally performed by the user, and there are some export prerequisites if you want to be able to have legends for example (proper UV unwrap of elements, and types as a texture. Also, you could export other data this way, like roughness, glossiness, color, etc).
You could have the keys pre-made as models in Blender, so your design tool just exports an OBJ full of empty objects with origins in the right place (or cubes, kittens, candies or whatever), and the script/addon populates this file with assets from a pre-made library, say, based on the item names. Item names in Blender can pass data with them (like legends, font type, placement on key, etc).
Scene is set up automatically, all you have to do is position the camera. Blender can do that with first person shooter viewport navigation. You just WASD into position and hit F12, Cycles magic happens.
Blender uses Python for scripting. You'd either need someone with Python 3 knowledge and enough time, or ask around BlenderArtists forums. Commissioning addons like that is habitual, and many of them are bundled with Blender as a result. Stuff like this should cost around $200-300 to develop I think, unless a fellow MK freak appears or sth.
If you think it could be an important tool that many people need, and would like my help, please start a new thread checking for interest with above info, and PM me the link. If there is sufficient interest (say 10+ people), I'll whip up a tech description for something like that, and assist with finding a dev if it's necessary.