Some suggestions for such a machine;
1. Keeping width around 27~28 cm, 30 cm would be too wide
2. Keeping depth around 42 cm, anything deeper would be too deep
3. Keeping height less than 40 cm
4. Make it with E61 brew group, with ECM details, like your bigger machines has
5. Joystick levers for steam and hot water!
6. To make it this small, you will probably have to place the gauges at bottom instead of at top, which is fine
7. Brew pressure gauge would be so nice
8. PID/shot timer!
9. Stylish cup rails, preferably integrated into body like the Technika IV!