For those regulations, there is also the important aspect of free cooling, i.e just using outside air as a medium or using an air-air heat exchanger like a Tokyo Wheel. Mandated heat reuse (without appropriate exceptions) would make those illegal, however in certain situations those are the best (environmentally and financially) methods of cooling. E.g. in a moderately hot summer you can use 20-30°C outside air without a problem, but if you would mandate heat reuse at that time, you would have lots and lots of excess heat on your hands with nobody buying it. So while some regulation will be coming, I hope and think that it wouldn't really issue a strict mandate to reuse heat and allow free air cooling, which would exclude direct water cooling.
To my understanding, DCs use air conditioning systems for cooling. These are already heat pumps - why would it be more difficult to just pump that heat into district heating instead of outside air?
Economically the greenhouse would have a distinct advantage of using free heat, and already having enough electricity wired nearby.
This, of course, only makes sense during cold seasons, or somewhere like Alaska or Sweden. During hot months, 40-50°C of heat seem completely useless.
Maybe next to a sea such waste heat could help evaporatively desalinate seawater, while cooling back to reusable temperatures.