Tankless water heater on the wall can be ugly. Reduce the beautiful-ness of your house. They are really square and boring. But we need it to supply hot water to whole house. It can not be replaced by boiling water on kitchen with cooking stuff. No no no, they are really square.
Thinking out the box, decorating the wall with electric tankless heater inside it is real possible. You can create something with the device as point of view or as a part of interior decorations. The idea is simple, take it whatever they are. Just accept their existance, add value on it and explore it. Some people will think I am crazy, but they never try it. Take back here, and do not comment until you do it and share the photos of interior with tankless on it. Oh ya, you can check the best tankless water heater to get some inspiration.