In X-4 (if it goes ahead) I think should be a fresh start, by that I mean veteran characters from the first 3 films should either not be in or have cameo appearances. Wolverine has had his screen time and with his own film coming out I cant see much cause for uproar if his character is significantly reduced. Storm is difficult one, I am not a fan of the storm we have seen in the first three films so for me it should either be:
1. Write out the character, or turn her into a cameo.
or
2. Re-cast and do a total overhaul of the character, make her more empowering and authorotive and please no cheesy lines for me it just isn't storm.
Beast is a character I would love to see more of even if it is just a cameo apperance, he was one of the best characters in X-3. I think Magneto should also be left to rest now, he is my favorite character in all three films but I think most of us will agree its time for a new villain, now if Erics was to return in a non-villain role that is a different matter all together
From the final scene in X-3 we know that Charles is still with us so its likely that he will return to the school which is fair enough, the X-men are his creation after all. It would be good to see both Charles and Eric leading and teaching the new team. I think that Bobby should definatley be in the next film, in X-3 we saw the beginnings of the more mature Bobby (although it would be nice to see his joker side as well) I think he should be promoted through the X-men ranks to be the leader in the absense of Scott/Jean/Storm. If they went with option 2 in my section about storm she would be leader and Bobby would be second in command.
Rogue for me is another character that either needs to be dropped or re-written. If she is written out I would be disappointed as she never really reached her full potential, since X-1 the character has steadily gotten worse IMO. If she stays in she needs her full powers. I have seen a great idea in another thread that she could gain her powers from ms marvel who could be a teacher/student at the school this would be a great idea and would give us the rogue we all deserve. Also Anna needs to stay on as rogue as she has done a great job so far.
One thing that is for sure is we need more colossus screen time, the guy is a great character with fantastic powers. It would be nice to explore his back story a bit and learn more about the guy, if you haven't read the comics but you have seen X-2 and X-3 you must surely be wondering about this guy's past, characteristics etc. Shadowcat was another plus from X-3, her powers were brilliantly portrayed on the big screen. As I said about colossus I think we need to know a little bit more about her back story something short like a small scene showing when she first learned about her powers.
Next we have angel, he served his purpose for the story of X-3 but the character was extremely underused. It would be good to see him as an X-man in a battle with his team mates. Now onto the big one....Gambit, many want him in and it could work. If Gambit was in he would have to be one of the bigger characters due to his personality. It would be interesting to see him in the team when he is such a loner, watching him ignore orders and doing his own thing. Also the relationship with rogue would be good to see especially if it is like the comics.
We don't want to see a character overload and no development so I think to balance it out and give each character its fair share of screen time and development the team should be something like this.
Definates
Iceman - Has to be in, great character that has been built up briliantly and now deserves a starring role
Colossus - Great character, totally underdeveloped. Needs to take over the hard man role from wolverine (action wise not character wise)
Shadowcat - Brilliant in X-3, needs to be in another film
Charles Xavier - Would an X men film be complete without him?
Maybe/Likely
Beast - Great in X-3 deserves another film
Gambit - Fan favorite, great potential for the big screen
Angel - Underused in X-3 could be a great character, needs an action sequence
Storm - Only if she is re-cast and the character is rewritten
dispensable
Poor choice of word I know but you know what I mean
Rogue - Unless she is given her full powers and a bigger role then her part in the story must end.
Wolverine - 3 movies and a spin off its time to call it a day.
Cyclops - I sometimes wish that he was left out of X-3 so he would have a chance to return, X4 would be his film. He could return as leader and be given the screen time he deserves.
Jean Gray - Has also had her time, I don't feel she could offer anything more
Magneto - Would be good to see in a teacher role with Charles but he should not return as a villain
Going on this I would make the team:
Storm
Iceman
Shadowcat
Colossus
Gambit
Angel
Charles returns as teacher
Beast cameo
Rogue cameo
Magneto Cameo
Cameos could be anything from TV appearances to telephone convos.
Sorry this is so long guys, I just wanted to get my thoughts out.