Sorry for the late reply I’m currently busy working on updates and other projects for the site at the moment….which is why I haven’t been on the forums lately (in case anyone is wondering).
1. Your theme will still work with Genesis 2.0, you just need to make sure HTML5 is NOT enabled. By default it won’t be if you’re using an older theme. So you’ll still be able to use it as you can see here from the Developer himself – http://www.nathanrice.net/blog/genesis-loop-hooks/
“Note: if you’re using Genesis without HTML5 activated, all the old hooks and markup work as before. Genesis 2.0 is 100% backward compatible.”
Also check his comment on backward compatibility – http://www.nathanrice.net/blog/genesis-loop-hooks/#comment-2076
“At some point, not sure when, we’ll remove the backward compatibility and only offer auto-updates to people who are running a theme that supports HTML5. It’s just the way it has to be … we can’t litter the Genesis source code with conditionals for infinite backward compatibility forever. But before we do that, we’ll update all the StudioPress themes to work with HTML5, and will probably maintain the 2.0.x branch for a year or so with security updates, etc., so you’re not caught with an insecure version of Genesis.”
2. The old version should still work with Genesis 2.0. The new version of Optimal will only work with Genesis 2.0. There’s no reason to create a new version that works for an older version of the Genesis Framework since no one will be or should be using the old version of Genesis. It’s always recommended to use the latest version of Genesis even if you’re using an older child theme for security and many other reasons…..you probably already know this, but I’m sure others may be curious.