Weather radar is actively being looked at by NATS but there are VERY few COTS examples out there. EHAM has one which is displayed on the radar screen and on SIS. However that type of display may prove very difficult to implement because the regulators will undoubtedly take a keen interest in displaying something which could potentially mask the primary function of the radar display, to show aircraft targets.
The other difficulty is what exactly do controllers think that a weather radar will display? Yes it'll show a grey area where there is bad weather but what does it mean? Is it simple precipitation? Is it huge CB's? Can aircraft fly through it? There is (
AFAIK) no simple way to determine exactly what the 'weather radar' is showing you.
Lastly, other posters have touched on the point that some companies and pilots may disagree with an ATC implemented restriction on where they can fly due to 'weather'.
BD