A tradeoff has always existed between the water temperature at which hydronic heat emitters are sized and their cost. The higher the supply water temperature assumed by the designer, the smaller the required heat emitters and the lower their installed cost. This is why the heat output tables on some baseboards did, and in some cases still do, list heat outputs at water temperatures all the way up to 240˚F.
Although I’ve worked with hydronic heating for more than three decades and designed systems around just about every possible heat source, I would be hard pressed to predict what hydronic heat sources might be available 25 years from now. Fifty years from now I doubt that I will be predicting anything. Yet I hope that hydronic heating, in some form, will still exist and may even be the dominant method of heat delivery.