The key problem I see w/your suggestions is the over-dependence on the community making the game into NFL-lite. I don't see how it benefits 2K in the least to base the appeal of their game on how much it can be molded into an ugly cousin of the NFL. For the person out there that has to have the NFL teams and players, it would simply make better sense to purchase Madden. I've said many times people underestimate the difficulty in trying to develop a non-licensed football game because of how the NFL is synonymous with pro football.
It think it's safe to say that the vast majority of people that would purchase the game aren't going to want to spend their first eight hours of the game customizing it to look/feel a certain way. And it's extremely wishful thinking to think some community standard will eventually evolve and people would have the 2K NFL game they desire. While APF2K8 was far too restrictive and needed more customization options, 2K was right in trying to make a game that could stand on it's own. Because I would think most people would want to pick and play a game they purchased; not spend hours/days scouring the internet for the person that happened to create the best Buffalo Bills logo, or who has the most exact 49ers roster. Only the ultra-hardcore are going to do that, and catering the game to that extremely small and finicky demographic would doom it to failure. As if the game wouldn't have enough obtacles to overcome.
2K made a lot of bad choices with APF2K8, but they did a lot right too. Off the soapbox, my suggestions on improvements:
1.) Keep the legends, but develop some sort of visual standard for them. Some looked entirely too old to be putting on a helmet. Also allow for generics to have legend-like abilities, as well as having "regular" generics. So players that aren't necessarily legends (like Tony Nathan) aren't overvalued.
2.) Blow out the sig styles on offense and especially defense
3.) Much needed improvements to the directional control/acceleration/momentum system
4.) Improve the single player experience with additional customization options/some sort of franchise mode
5.) GET RID OF THE TOTALLY UNINSPIRED UNIFORM CHOICES. That single improvement alone would've enhanced the first game's visual appeal. There were tons of community uniform suggestions before the game released; they could easily make it a community thing and have them vote on the best uniform/logo choices. Or hire Under Armour to design the unis since they do a great job with uniforms.
6.) Improved player customization options, less restrictions