the reason for "only" 512 SSDs is that is the i/o limit of the system. 3PAR doesn't want customers to be able to oversubscribe the controllers/ports with more I/O then they can handle.
The limits have been well documented by them ever since SSDs were announced, though made more public since HP bought them since HP publishes the specs on the interwebs
Increase in maximum number of solid state drives (SSDs) in HP 3PAR P10000 Storage:
* The maximum number of SSDs has been increased to 128 per node pair
* This translates into a maximum of SSDs of 256 for the V400 and 512 for the V800"
For the older T-class
"* Minimum of 2 SSD magazines (8 drives) spread across a minimum of 2 drive chassis on a given node-pair
* Maximum of 8 SSD magazines (32 drives) on a given node-pair
* Minimum of 1 SSD magazine (4 drives) per drive chassis
* Maximum of 2 SSD magazines (8 drives) per drive chassis"
The all SSD offering is interesting, since before it was not a valid configuration(not sure why other than probably no customers would get it). Though interesting to see the results, wonder when they will get officially posted.