I generally share the same opinion as Trax. Much of ROM Hacking is so game specific, I'm not sure you'll find enough commonality to make it worthwhile.
Much of what Gemini describes, while useful for C++, is already covered with the .NET framework out of the box.
What's left is the ROM hacking specific functionality. We've got some things such as handling tile data in various formats for older consoles, TIM for PSX, and whatever might be necessary for platforms I don't follow closely. Dumping and Insertion functionality. Table library. Maybe a compression library. We have a serious lack of library for doing anything sound/musical related on nearly any platform. Some code for handling virtual file systems and dealing with isos. Address/Offset conversions. Header functions for those consoles that use them. Those kinds of things.
So, there is some ground to cover, but if you're delving into all those areas, you'll do everything on par, but nothing great. A dedicated tile editor, script dumper, sound utility, vfs utility, that's fully developed and expanded with code would likely be much more useful than some framework code for dealing with a little bit of what they do. It's also unrealistic to really have framework code covering all the things I mentioned well. That's too large a project for one. Although maybe you could pick up some more developers as you go.
I don't want to discourage new creations at all. It might be worthwhile to you and/or others. Just in my opinion, I can't say I think it would be that useful or worthwhile. I have found it difficult to find a lot of reuse for my own code from project to project. You really need to get that design and abstraction level very high and broad to end up being useful from game to game. And when all the work is put in to get there, you probably could have just done the specifics for projects several times over!
My advice to you would be this: Start on paper. Start writing out a design plan and framework hierarchy. Figure out the design and outline of what you intend to do. When you've got something, people can probably give you some feedback. I think this would be a very ambitious project to do right and be useful.