Been waiting for someone to develop something similar to this for a long long long long time and hope you can keep this project alive. I've been using a company called esportsdesk for quite some time and while it does a good job I never have access to where my site is hosted and the system is very template themed. Having the ability to create my own site and own design with this plugin would be a HUGE benefit.
Some things from personal experience from using that system would be (and some have been mentioned)
1. Widgets, team standings, league leaders (stats), player(s) of the week/month etc, a schedule/latest results widget.
2. Agreed with what was mentioned about setting it up so users of each team can login and update the scores. What we have set up with our league is the home team of the scheduled game inputs the gamesheet into the website and each has their own user/pass to do so.
3. I havent had a chance to install this locally but on our schedule played after the game details have been entered the date then becomes a hyperlink and leads to the game details. It's a nice feature, that or a link in the table next to the game in question saying details.
Those are just some of the things I can think of off the top of my head. I see great potential in this plugin and am surprised no one has took it upon themselves to do so. As hard as it is I hope that it wont be designed with one sport in mind (I see a lot of Soccer references). I currently run about 4 hockey sites and have been waiting for something solid like this to come along, but so many sports have different scoring systems. We have 2 points for a win (regulation, OT, or shootout), 1 point for shootout or OT loss, and none for regulation loss.
I think if you can find a way to accommodate a bunch of sports you'll have a sure winner here.