But she's the new one you need to explain everything for the benefit of the audience. And give the fan-boy point of view. At least on this show the obligatory Voice-of-Whedon nerd has aesthetic appeal. Speaking of which, there are about two hot chicks too many for a Whedon show. Usually his actresses are more of the "attractive" category than objectively beautiful. They don't have standard good looks, often odd or different features that they make work, but still allow them to pretend to a degree of regular-people qualities. Sarah Michelle Gellar, Eliza Dushku, Amy Acker, Jewel Staite, Amber Benson, Dichen Lachman, etc. The Hollywood-hot actresses tend to be villains or antagonists, at least at first, like Julie Benz or Charisma Carpenter or Christina Hendricks or Stephanie Romanov. Ivana Milicevic showed up as an ex-boyfriend's wife. Yet those last are the kind of looks that we are seeing in Skye & Mei and the British chick. Not to mention Colbie Smulders, whose own TV show is in its last season, so if Agents of SHIELD makes it to season two, she'll be free for a full-time gig. It makes me wonder how much authority Whedon had over the casting, and if other forces were weighing in with "No, prettier!" orders, in what other ways might they be interfering?

A happy alternative, of course, is that maybe this is what Whedon wanted all along, and only now does he have the budget to hire all hot chicks.

I don't think he'll be in the next one. Maybe his comatose body or floating in a tube or something, but he's probably going on a shelf while they work out how to fix or cure him. A guy with real super powers doesn't really fit into the dynamic they've established, and they're probably going to take a while to do more than tease with that. Buffy & Angel took a few years to start giving the non-titular characters powers, and River didn't really become useful until the movie. They don't want to unbalance things, but I think Richards will be around some more down the road because A., there's no other black people and B. there aren't any Whedon vets. Also, on Whedon shows, there have been actors who were significant characters for years before they became regulars. Amber Benson only was listed as a regular for one episode, after being on the show for most of three seasons, and that was the episode where her character was killed.
He could, for the reasons I gave re: Richards.
I think that stuff has to develop a bit more organically. Firefly was the exception with the way it hit the mark right off the bat. Watch the first season of Buffy and you'd be amazed at how far Whedon's come, and how that show got a second season, much less four more shows and two affiliated movies for its creator. As long as it gets time, that stuff has a chance to happen.

As far as the hopeful stuff:
Structurally, this looks to be playing to Whedon's strengths. He is much better at the ensemble dynamic, with a disparate group trying to do their best against overwhelming odds (Angel, Firefly, Avengers). The genre deconstruction he is better known for works more in small doses, rather than as the premise of the work (Buffy, Dollhouse, Cabin in the Woods). On the other hand, he can get too caught up in his enthusiasms, and it is clear that the whole "secret group with cool toys and awkward young scientists and badass dudes who take pratfalls" concept is something he loves to play with, as it has turned up in one form or other on almost everything he creates, except maybe Firefly, where it would have if the show had kept running long enough. That concept was the focus of his worst show (DH), absent from his best (FF), subverted in his second best (Angel), and was the gimmick of the season in what is generally agreed to have been the worst season of BtVS. So he could totally bungle this one.

The other concern is that this is a corporate thing. IDK what the IP stuff is with the Avengers, or any of the behind the scenes or money issues, but Avengers IS owned by a big corporation and was successful on a huge scale, which is responsible for this show being a thing. The movie itself was the climax of a string of movies that set it up, and it is plain that their plans for the cash cow are still on-going as both subsequent films make reference to the events of Avengers. That raises the question of how much input the money people will have on the creative stuff for the show. And remember how I pointed out that Whedon's more meta stuff often doesn't work (or succeed in ratings/ticket sales on the same scale)? Well, you can pretty much pull a whole meta thing out of this show vs the movies and the agents vs the super heroes. The struggle of people in a world populated by demigods as a metaphor for a regular creative dude against the corporate sponsorship that is the whole reason for his project's existence in the first place, but could crush it like a gnat.

This is familiar territory for Whedon and his past track record shows he is more than capable of crashing and burning, or taking off, either one. And history also suggests that even his best work can be ruined by forces above his control. Are the Marvel moneymen going to be a sinister force for destruction the Blue Hand agents in Firefly, will they be a dangerous threat who nonetheless gave him the keys to the kingdom like Wolfram & Hart in Angel, or will they be benevolent and empowering like...um...absolutely no powerful group or force in any Whedon-show or film...? Uh oh.