That would basically be a complete DSO, except the output would have to be converted to X,Y,Z instead of LCD. It would need amplification, attenuation, triggering and sampling. The LCD is not exactly the most expensive or complex part in a modern DSO. Getting a crappy low-bandwidth/voltage DSO would probably make more sense.
Analog storage was the old way of doing it, they used a special CRT that would retain the charge from the trace for a certain amount of time. This technique is inferior to a DSO, though, and completely obsolete, as opposed no normal analog scopes.