You could do that though MaxMan777. You could create the underlying template yourself, submit it to the devs and I'm sure if it works fine, they'll probably include it with the other templates.
That's the closest you're going to get though, because I don't see there ever being some "American Football" behavior or object. Firstly one isn't required, secondly a lot of people wouldn't want it or use it, thirdly, such a thing will simply spawn a great deal of very specific games. The current behaviors are generally pretty open for use in different ways. But what you're asking for is too specific for a behavior itself (and a whole bunch of behaviors that aren't much use to anyone outside very specific single type of sports game will be annoying).
It sounds like what you're actually looking for is a ready made game that you can mod yourself, rather than make your own game. Can't you mod any of the games out there now, or is EA still making modding difficult for their games?
Also, even with all the rules of football, it doesn't strike me as all that complicated to make in construct right now. And I'm the first who'll jump in on a chance to prove construct can't do something, but this would be easy for it. Someone recently posted a cap they are working on with controls that could be used for some kind of ball passing movement. Player controls could be selected by distance to the ball without any problems. Scrolling is very simple to setup. Really, if I think something is easy in construct then it must be.
As for your choose your own adventure thing. You could make one of those insanely easily with just HTML and a tiny bit of PHP (the php for storing stats, inventory etc). Or make simpler versions using Mediawiki. If you're instead thinking about text adventures like Zork or The Hobbit. Then you're looking at text parsers, which construct can do quite easily too (I've spent time looking into this previously, as personal interest myself) or can be done online, again with PHP which has no trouble at all parsing strings.
I really don't follow this web thing you're after though. Are you instead talking about WYSIWYG? Construct already is. This web thing though, construct isn't a web page builder. It can GET and PUT files onto the net, update and change external files, but that's about it as far as web stuff goes. Though it wouldn't be outside the realms of possibility to make a html editor with construct.
And I'm with Ashley on the random expression thing being incredibly useful. I've come up with all kinds of crazy things in PHP using mt_rand() that you wouldn't think random numbers would be used for.