Yesterday I committed and tagged the v0.12 release of my WordPress Google Form plugin. It is available from the WordPress plugin repository. The main feature of this release is support for multi-page Google Forms. The changes made to support multi-page forms should also enable use of fields that have optional answers.
There is still some leftover code from the old validation process that I was reluctant to completely remove until I know for sure this new architecture is working in more use cases than I have to test with. There will likely be another update that is nothing more than a code clean up in a couple weeks unless someone reports a problem.