Will coefficient of performance rise in the future for heat pumps?
Absolutely they will get better! Every year company's invent new methods of controll that have increased performance, research is on going to find better forms of "Freon" that are more efficient and don't have a global warming or ozone depletion problems. How fast will it happen? Right now there are small increments of improvement every year and who knows someone may have a groundbreaking discovery that takes us to a whole new level of efficiency. Would I wait to purchase a unit for my home? No I would do it now, well I did do it to my latest home not long ago. The advancements are usually small but continual as each of the big players try to be the best so if you wait 5 years the rating of the best units may improve 1 or 2 seer. 20 years ago 13 was a good value now we are getting above 20- 22 with many mfg's. Note seer is seasonal energy efficiency ratio. The higher the better.  I use that instead of the coefficient of performance since seer is the standard comparison in the trade. To further answer your question we would need to know why you ask.