If PHP 7 deliver on the performance, which looks very promising already. Its adoption rate on the enterprise and professional level will be very quick even if they decide to add a lot of BC breaks.
I am surprised you do not put more weight on this, since it easily means thousands of dollars saved a month for anyone running a larger system. Even for smaller systems, it can mean the difference between having to move to a larger server, compared to being able to stay on the old one.