Because I'm bored, I'm posting how I think the teams powers should be upgraded. They have remained pretty stagnant compared to other heroes and it's past time that they got stronger,I hope Slott upgrades the team's powers.
Johnny
His Nova flame has been used so often that it's not very special anymore and doesn't stop the villains a lot of the time, so there needs to be some new things he can do with the power up. It would be really cool seeing Johnny doing some crazy stuff with his powers. Like his flames being different colours depending on the intensity of the heat which would be a nice visual representation.
Blue flames - These would be a stronger version of his flames and boost his powers in general, but especially his flight speed. The downside would be that it's hard to control so he only uses it in short bursts.
White flames/plasma - The strongest flames he can muster, it would be like him being covered in Nova level flames. Every aspect of his abilities on the level of when he had the cosmic control rod and he is immune to physical damage, but they come with immense downsides. He can't use it near of other people otherwise they will suffer severe burns and he can't maintain it for very long as it depletes his energy to dangerously low levels. After using it he can't flame on for a while so it's something to use only under the most dire of consequences.
I think these two flames would be cool to look at and the downsides means that he won't use them too often so that they won't replace his classic orange flames.
Visually when coated in blue flames they should look less 'wild' than his orange ones, like the flames on a Bunsen burner or stove.
(Here is the best visual representation I could find)
Ben
Ben is in the most need of an increase in power, he used to be able to hang with the Hulk and was one of Marvels strongest. He should be that strong again.
I think Ben's power should be at around Hulks level again I also think he should have some minor control over earth like his Secret Wars counterpart did as it was really cool. Having that plus his strength lends to the 4 elements aspect of the FF's powers and it also makes him different from all the other super strength heroes, there aren't many heroes with that particular powerset too.
If you weren't familiar with the FF and you look at Ben you wouldn't be surprised if he could control earth.
Reed
I can't see how to improve his elasticity any further, so instead I think that his gadgets should be incorporated into his costume like a utility belt or something. It gives him ready to use inventions and it also works as good visual storytelling to what his role on the team is. Let him fight using both his powers and his intelligence.
Sue
Sue is the least in need of a power-up imo, she just needs some more creative ways to use her powers. A particular one I like is her shrouding herself in a thin force-field to enhance her strength and defense while also simulate flying. It would be useful when she is fighting particular fast and strong villains and let her show off her martial arts more. The downside to it would be not being able to use her force-fields for other means at first because of the amount of concentration it would take. Also, more interesting uses of her invisiblity as it has taken a backseat to her more bombastic force-filed powers.
P.S Franklin should be de-powered when they come back as a result of overusing his powers. He shouldn't be completely powerless, but he should not be god-levels until he's an adult. It stops him from being used as a deus ex machina.