That's one thing that sort of annoys me with the Smash fanbase. A lot of people have forgotten what it's like to be a casual gamer.
I knew who Joker and Terry were before they were revealed. Granted, I knew virtually nothing about them, but I still recognized them. If someone were to tell me that they had absolutely no idea what Persona was or what game this weird Joker fellow came from, I could understand why. Same with Banjo, Terry, or any of the characters in the first pass really.
The Smash fanbase on the other hand expects you to match the knowledge of a teenager who stops by Gamestop every day after school so he can exchange old games for new ones. You've clearly been living under a rock your whole life if you didn't know about Bayonetta and her two games prior to her reveal. Who DIDN'T play Persona 5 when it came out? The whole world was talking about it nonstop, so there's no excuses for not knowing him. Oh, and everyone had an SNK console growing up, so Terry is pretty much the most iconic thing in existence.
What we define as iconic is completely different from what an average Joe defines as iconic. I'm sure several people in this thread could make a list with over 100, maybe 200 characters who qualify as "iconic". Other people might only be able to get half of that.
I get your point and I completely agree with your first line, but I don't know, I'd think that at least most of the Smash fanbase who participates in speculation (Smashboards, GameFAQS, Twitter...), which means they are usually informed about everything surrounding Smash Bros, are people that couldn't be really considered casual gamers.
Maybe we have different definitions for being a casual gamer, but in my personal experience the casual folks who plays Smash usually don't care about who gets in, if anything they're usually more open to any newcomer, even if they don't know about the character. At least this is the experience I have when I play with people who aren't really that dedicated as us.
The people I met just wants to play the game and have fun, they pick the character they like or the cooler one for them and that's it. Maybe they would like to see certain characters in the game, but those people aren't actively participating in discussions and supporting their most wanted on the internet just like we do.
About the rest of your post, well, maybe there's some people who acts like that but I'd never expect everyone to know Persona or Bayonetta, even if both franchises are in it's peak of popularity. It's not okay to be mean to anyone who doesn't know about the upcoming DLC. I'd say that I was really surprised to see some people saying that they never heard of Dragon Quest, when DQ is usually featured in Directs, but that's another discussion I guess.
For example: if for some reason FP7 ends being Sol Badguy from Guilty Gear, I'm not expecting everyone in Smashboards being familiar with him or his series, the same would apply, of course, to casual gamers, because Guilty Gear (and most of franchises out there) isn't really mainstream. That doesn't mean it's not popular in it's own way, but I wouldn't act like a jerk because people aren't aware of Sol. That's just unnecessary.
When I talk about this subject I always meant that what I'd like to see from the Smash community in general is more respect. Even if you don't know the character or you didn't like the choice, I don't think it's cool to be angry with the new character and his fans or spam "literal who". This applies to any caracter, no matter if it's super popular or an unpopular one.
Just like I don't think it's fine to act as an elitist and an arrogant because people doesn't know about your character, I don't believe that being disrespectful or obnoxious with characters or franchises you aren't really familiar with is the way to go. Both things are equally bad in my eyes.
I just think people should be more nice in general.