I'd strongly advice to think it through. There are many Kanban/Scrum tools already - here you can find pretty comprehensive list: http://www.limitedwipsociety.org/resources/tools/limited WIP society tools
Also, when we're discussing Kanban many teams tend to work with physical board and not software as long as that's possible. But of course there are also those which can't and have to fall back to some kind of application.
Anyway, for me this niche looks pretty crowded already and unless you have a good idea for differentiator - something which would make distinguishable from others and would the best of breed at least for some specific group of end-users (teams) - it doesn't sound like the best app you can build.