You have to remember that enterprise level storage isn't a single set of drives holding the data, it's a hierarchy of different technologies depending upon the speed of data access required.
Since SSDs arrived they've been used at the highest access rate end of the spectrum, essentially using their low latency for caching filesystem metadata. I can see that now they are starting to replace the small, high speed drives at the front end entirely.
However, it's going to be some time before they can even begin to replace the storage in the second tier and certainly not in the third tier storage where access time isn't an issue but reliable, "cheap" and large drives are required. Of course, beyond this tier you generally get on to massive robotic tape libraries anyway, so SSDs will never in the foreseeable future trickle down to here.