We'll see when we get there, right now I'm not seeing A3 consisting of all of those heroes and like I said if it does Thanos will quickly make half of them irrelevant. At best they could go for sending off the old and bringing in the new if Falcon, War Machine, Ms. Marvel, Strange, BP, Ant-Man, etc. are all gonna be in A3 (again which I doubt) but I still think a story like that would require a multi part movie not just one.
Again, it's not the fact that they'll be in the film for a minute for 30 seconds or 45 minutes, it's the point that they'll be in the film and have to be fit in somehow. While over at DC, they are being lambasted over 3 confirmed characters (one still likely a cameo) plus the rumors of 2-3 other characters (which are also likely cameos as well).
What do you mean "fit in somehow". S.H.I.E.L.D is well established in the movies. That's a handful of the characters you listed already. I do not think BP, Strange. or Ant-Man are gonna be in Avengers 3 so I'm not seeing how hard it'll be to fit in the remaining characters. The way it looks it'll be the Avengers, SHIELD guys, and GOTG up against Thanos w/IG, one or two lesser villains probably cosmic/aliens, some cameos by other villains, and his army.
Ms. Marvel isn't showing up in A2 as Ms. Marvel. I fully expect set up and introduction, I don't see anything kree related in A2 coming in so she'll probably just be another SHIELD agent. So unless they change her origin and tie her to Ultron I expect her to become empowered in A3 as of what little we know now.
The reason DC gets ******* on is cuz they really do seem like they can't do something simple and good. Marvel has the structure and proven track record cuz of the way they led up to Avengers. It'd take a few terrible movies to change how they're viewed. DC went from one okay MOS movie which ended with either ppl who loved or hated it and for those who loved it they looked forward to a really good and better world building sequel, hopes of Lex and what not. Instead it appears DC went for trying to catch up to Marvel too quickly with Batman vs. Superman, something they knew would drive fanboys crazy and generate a lot of hype and (even when that was announced I wasn't as happy as I thought I'd be) that could've been good enough but no that wasn't enough, just to try and hedge their bets cuz A2: AOU is probably gonna gross $2-4 billion they've turned an MOS sequel in to a Bats vs. Supes flick and now to a JL lite movie cuz they're impatient.
Simply put DC has a lot more to prove. The fans already have faith in Whedon, Fiege and Marvel. Not so much for Snyder, Goyer and DC. So you're gonna get criticized for every little rumor and every official announcement from ************* Jesse Eisenberg as Lex Luthor to WW going undercover in Wayne enterprises to get some artifact or some bull **** that belongs to her family and other **** like Aquaman not being called Aquaman but blah blah. That's how it's gonna be until DC makes a great movie in their new shared superhero universe.