I don't disagree that people may well mod them, but I really doubt it'd be worth doing. You could replace the block, but then you may need bigger tubing, new coolant, and since the pump is in the block, a new pump. You'd still have a tiny £50 rad though! That's why I think it'd be a waste of time, you'd just be buying a new watercooling setup anyway.
My realistic prediction for this product is that it won't offer anything more over high end air cooling apart from perhaps being slightly more quiet, though the hum of the pump or similar may be even worse. I think it'll probably be best left to OEMs and n00bs who just want to say they have watercooling in their PC, but it won't catch on as an enthusiast product.