Drop OpenGL and port it to D3D9.
OpenGL on integrated graphics is getting better for sure, but it's still not in the same league as D3D for robustness of driver quality and all-round general predictable behaviour. D3D will give you (and - importantly - your players) a much more stable, solid experience and with less driver weirdness to have to deal with on integrateds, you'll be able to access features that are just not available with their OpenGL drivers (such as high-level shaders), and you'll be able to target machines with OEM drivers that don't include OpenGL support. D3D9 in particular will enable you to hit even older Intel GMA class graphics with a reasonably full feature set.
On the other hand, and being a little more serious, I'd suggest that you're spreading your target hardware too wide. You're talking several generations of hardware and at least an order of magnitude difference in performance, and you want to get the best possible out of it all. Even with the best will in the world that's just not going to happen; nobody does that, not even major game studios with huge budgets. So scale down your ambitions and pick a more realistic and achievable goal instead.