Fr4 PCB is mostly used in pcb manufacture. Fr4 pcb is mainly used in double side pcb or multilayer pcb. The cost is much expensive than Fr1. Nowadays more and more prodcut turns to use Fr1. Do you think Fr1 would go to replace the Fr4?
Obviously , the answer is no. Fr4 is more advanced material in products. People would consider the usage of the product to choose the suitable material. Although the price is main factor to effect the choice, fr4 has its special usage in the pcb production. Fr1 is used in very simple products. Actually, fr1 can be only used in single layer pcb. If you look into the products you may find that the electronic is more advanced and many of them is above 2 layers. Now the requirement of high technical,high density is in the current world. So fr4 would never be replaced by fr1.
Fr4 pcb has the following advantage:
Good mechanical strength and excellent workability, good mechanical properties, abrasion,acid and alkali.