Making the 144k figurative doesn't mean they'd suddenly have to believe everyone is going to heaven. They would keep their two-class system, and just put heavy emphasis on the 144,000evidently meaning the number of Christians with a heavenly hope would be a very small subset in contrast with the "great crowd".
The concept of paradise earth is one of the most appealing aspects of the Witnesses to the majority of those who sign up. Thus, you'd still have the vast majority holding to that hope. The percentage of partakers would definitely spike, no question. But I think it would stabilize rather quickly. Probably no more than 5%, quite likely less than that.
Stop giving them ideas.