Tried out the new survival mode last night. On Vita I was able to play it "solo" by creating an ad-hoc match and starting the game. It then paired me with three CPU partners.
On PS4, I didn't see a way to do this but found a game to join, hosted by a Japanese player. We waited a bit but nobody else joined, so when he started the match, two CPU partners were added.
This mode is pretty fun. It's totally tower defense -you get a shrine in the middle of a stage that you have to protect- and waves of enemies come from different directions (we played on the beach stage and they kept coming from either side). Although most enemies will go down easily, the swarms are large enough that enemies will get past you and aggressively go after the shrine, which loses its energy very quickly, so it can be challenging once you get waves with the more advanced enemy types. The AI partners we had were generally pretty stupid and didn't do much to help, but we managed to get to wave 30 or so before we lost.
As you play this mode, you unlock rewards in the form of badges, which are the same little head sprites you see when cycling through character to select on the level select screen (and the censor sprites from SV, lol). I think these can be used as accessories, but I'm not sure. This mode also displays your character's super move animations and seems to limit air combos.
Also noticed that the options menu has an option for Shinovi Versus music, but it was greyed-out. Assuming this will be DLC.
Finally, I think a new multiplayer versus level was added, but I didn't get a chance to check.