I think what will happen is that PS3 players will be given an ultimatum to switch to the PS4 or PC if they want to play Stormblood, otherwise their game client will be updated to V4.0 but they will never be able to go into the Stormblood areas, they aren't optimizing it to run on it.

Faster mounts typically require MUCH faster network connections, let alone disk read time. For a different mmorpg game that I had contact with developers for, the developers could program whatever speed they wanted into arbitrary gear in the game, but if you actually ran at the speed of sound in the game, your "draw distance" and "pop-in" 's happen every 3 seconds. So you would overshoot just about everything, and because certain parts of the map aren't loaded into memory, the server basically says "your speed is zero from running into a wall" but your game client still shows you running up a mountain for 10 seconds until rubber-banding back to the wall your game client thought you phased through because it didn't load it in time.

I doubt we will have mounts that run at 800mph, but the fact is that if you move faster than the disk/memory/swap-file can catch up, you no longer get a 30fps/60fps experience, you get basically a blank screen, or empty-zone between your start point and end point, and only once you stop moving does the game load from the disk and all the characters pop in.