Several decent distance runners have switched to cycling and done pretty well. That being said, cross-training between several sports to increase performance in one particular sport has been pretty well discredited.
Plenty of pro cyclists run in the off-season, but once training is underway that all ends. Like any physical activity, the body adapts to repetitive motion with muscle memory and synaptic efficiency. That is why pro cyclist train for hours on end even if they are not riding hard.