I am expecting that the patch with new modes will come with higher caps so that they can entice players again.
Like, seriously, all they need to do is release a blaster with a sprinkler. I don't care if its rate of fire sucks ass and it has echolocator, I will legit use it for that main/sub combo alone.
EDIT: Just finished the single player campaign, and I'm shocked at how quickly I've burned through every part of this game. However, it impresses me that it was so easy to become absolutely consumed by a game like this. If there were any more content I'd probably be devoting a whole lot more time to Splatoon, but seeing as I've capped at 20 and am now simply awaiting new maps (like the bridge level from the single player campaign, someone, somewhere also mentioned a sort of log-cabin themed level? It was also in the footage from last year which changed quite a bit), weapons, and modes to keep me playing the game. This will go from a hungry quest to a game I play to de-stress, which is okay.
I would agree with all those who say it's light on content. My main worry, and something I have voiced on other channels, was this- once Nintendo decides to end Splatoon's online play, how much of a game will be remaining that I really want to keep? The answer is almost-nothing, and that's a bit disappointing. I would be very open to more single player levels, but I'm not going to hold my breath.
That final boss was pretty silly, though.