Hi! New ninjas are released with new updates. There is currently no estimated time as to when the ninjas are released but there will be an update if they do. Usually, new ninjas must be approved by the copyright owners of the Naruto franchise before it is processed as a new ninja. In regards to your initial question, I haven't heard anything in regards to a new version of Tobi.

~Jib

Jib Edit: Hopefully this sheds some light on the process, if you do have a suggestion on a specific ninja you c*e the "Suggestion Thread" found here.