You assume Arabs will vote for "Arab" parties. Many Bedouins vote for Likud. Arabs account for around 35% of Labor's vote as well. Arabs are not cohesive. Druze and Bedouins hate Palestinians intensely, so intensely that army units including them can not be used on the West Bank. What you are really asking is whether nationalist Arabs will reach that level, and that is a question that involves questions other than pure demographics, and assumes that identification will remain the same proportionally over the next 30 years which is not clear.