I'm in the same boat!
I switch from a Macbook/iPhone 4S to a Google Chrome OS/Samsung Note 2. I am feeling the same way and looking to go to back to a Mac OS ecosystem because GTD is so important to me and my productivity.
I have trying to use todo.txt since it's very simple but it's organization is getting difficult with all of the projects and someday maybe lists that I am creating.
I have not been able to find out if OmniGroup is creating anything but I know David Allen Co. has teamed up with another company to develop something.
I just might go back to my iPhone!