Here's how I would want to see the Fantastic 4 in the right hands...
The Cast:
David Schwimmer as Mr. Fantastic/Reed Richards
When it comes to looking like Reed, he certainly has that in the bag. Obviously though, what matters is if he has the acting chops for the role, and he does. He was nomintaed for an Emmy in his role for The People vs OJ, which is impressive to say the least. Personally, he just gives off the "nerdy, workaholic, confident" personality that Mr. Fantastic has.
Elizabeth Banks as Invisible Woman/Susan Storm
Just to mention before I get any further, I'm going for an older cast on purpose. I think the Fantastic Four should be seasoned veterans rather than origin story rookies if they get rebooted again by Marvel. Anyway, Banks seems like a perfect choice for Invisible Woman. She's got the skills to carry the role, and the looks for some major eye candy. And considering she's been in all three Spider-Man (Sam Raimi) movies, and even played a villain in the recent Power Rangers movie... I'm pretty sure she wouldn't mind playing a supeheroine. Not at all, in fact.
Dane DeHaan as The Human Torch/Johnny Storm
DeHaan definitely would be a more than adequate Johnny. He can pull off the cocky, laid back character, and he looks similar enough. I, personally was extremely impressed by his acting in Chronicle and The Amazing Spider-Man 2. So he's a strong actor without a doubt.
The Big Show (Paul Wight) as Ben Grimm/The Thing
Yes, he's a WWE wrestler. And yes, they're usually not known for breath-taking Hollywood performances. However, I just got a feeling the Big Show could do a good, solid job. It wouldn't make much sense to go the actual makeup/costume direction for the Thing again. So, CGI a la The Hulk and Groot would be better, and generally much easier. He could provide a deep, booming voice for The Thing, as well as do some motion capture, considering he's a legitimate 7 footer.
Noah Schnapp as Franklin Richards
Coming off his hype train from the Netflix hit Stranger Things, studios will definitely be looking at him for roles. Marvel should be one of them. Since this is an older Fantastic 4, it would be nice to introduce Franklin Richards to the big screen for the first time. In terms of resemblance to the character, it's just fine.
The Story:
Let's be honest, no one is going to want to see another origin story of these guys. Like I mentioned before, this would be veteran type Fantastic Four. To the point where actually they're all retired from hero work in the beginning in the movie. And since this is Marvel's First Family we're talking about, imagine if they were the "Avengers" before the Avengers? You know what I mean? They were stopping catastrophic disasters and supervillains way before Iron Man had a team. Or even before he was Iron Man. That's what I'd like to see the MCU start the movie like.
Villain wise, it'd be interesting to see the Mole Man. Let's say he's causing trouble in a completely different country, and that alone brings the Four back together. It just makes zero sense to have Doctor Doom be the main villain again in the first movie. He's something you build up to slowly but surely. Maybe they can name drop him time to time, and set it up where he's not making any problems for now.
The Director:
Brad Bird or Sam Raimi. Simple as that. Those two could bring a light tone to the F4, without it being too corny (well, I have more faith in Bird than Raimi on that one).
Conclusion:
21st Century Fox at some point is going to make a decision on the F4. Right now, they're just sitting on their shelf collecting dust. It's highly unlikely they make a sequel to the last F4 movie. And it's even more unlikely they reboot the franchise again themselves. If they're smart, they will give the rights back. The fans won't see another F4 movie created by Fox, so they might as well give it to the company that gave them life in the first place. Marvel.