The known technical limit would be
240W USB PD charger.
Top-end Mac Studio M1 Ultra
5nm has a
max power input of 215W without a display.
A M2 Ultra
3nm with at least a 20% performance per watt improvement would allow an Ultra in a MacBook Pro with 240W charger.
The question would be how big of a market is there for laptop that sells for nearly $7,000 and weighs nearly 2x 4.7 pounds (2.1 kg).
Mac Studio M1 Ultra's heat sink fan was made of a more thermally conductive material that weighs more so it can maintain its heat sink fan's RPM and physical form factor dimension.
As the M1 Ultra chip is 2x the die/surface area of a M1 Max chip then the heat it generates would be 2x as well. So that Macbook Pro M2 Ultra 3nm would run hotter than the top-end Macbook Pro 16 M1 Max.