I guess it depends on the client, if he is willing to take the risk that, for e.g., his app won't be compilable with the final version of RubyMotion. You can probably convince him it is a good idea if you specify in your contract that you will offer support in the future when RubyMotion for Android is stable.

I think RubyMotion could be a good idea, even today, for someone that knows and use Ruby for his own projects.