How so? It would allow me to use a 50mm f/1.4 to shoot surfing footage just before dawn and after dusk. This is often the best time for quality waves, especially in the best locations like Hawaii, Indonesia, Mexico etc where daytime land/water temps cause onshore winds during the daylight hours but you get favorable offshore winds when the sun is hiding - Not to mention the dramatic lighting and colours you get at these times. a 300mm f1.4 which has a deeper dof than it apparently should? Thats one artistic choice I would like to have!
As a practical matter, there are very few (any?) 50mm f/1.4 primes that would give you satisfactory results with the fine pitch of a GH1 or similar sensor and the lens wide open. You'd probably have to stop down to f/2 to get good results. That is unless "good" for your purposes happens to be a very soft and even "glowing" effect. In that case, you'd love the results.