I'd love to see a website that had interactive training and tutorials. A lot of great minds in FIRST have put a ton of time into generating presentations for conferences and their teams, but its often only available if you attend the conference, or you can find the videos or slides online, but its not the same as getting it in person.
Many years ago, I wanted to develop an online "FRC Certification" database that would make use of some of these presentations and incorporate some "tests" or interactive tutorials that would quiz the viewer to see if they understood the material, and then they could get a "grade" in the end, indicating if they have grasped the concept.
At the very least, a website that collects a ton of trainings and does a good job categorizing them would be awesome. I know
WPI tried to do this a while back, but I think the effort died down after a while. FIRST has done a better job on their
technical resources, but they are kind of component specific, rather than "how to build a swerve drivetrain" or some of the more creative trainings we've seen.
This may be beyond what you were looking to do, but its an idea I had a long time ago and never really had the chance to implement, and I think it could be incredibly useful to the FIRST community.
Just take a look at all of the websites that are out there for FIRST, and see if you can find a niche. There are a lot of sites that have tried to startup and have since died. The two strongest ones that have been around for quite some time are obviously Chief Delphi and The Blue Alliance. Don't try and duplicate what is available with either, its just extra work, and may make it much less likely that anyone will use your site. Instead, find something unique that would be helpful to the community at large, and once you have that and a stronger user base, you can add more features.
Good luck!