I would probably just recommend working on whatever you love
Ya, I figured this out with other failed ventures. I think you really need that implicit motivation/passion for something in order to stick it out for the long hall and really create an exceptional product, whatever that might be.
You could always augment your project idea to experiment with 3D technology more (even while keeping the gameplay 2D) as well (which might make for an interesting style!), if you want to flesh out your 3D game engine programming skills.
Ya, I've already been searching for games which mix these different perspectives and how they look. There's definitely a lot of interesting ways you mix the two that I'll have to explore deeper if I decide it would be worth it to add in the complexity of 3d in some way.