Yes, its natural to expect that MT4 maintenance will be stopped soon, because platform interface is very obsolete, something that was popular 15 years old or more. I think they have to stay competitive and work on newer version.I'm glad that my current broker Hotforex has already started to support MT5.
I heard that Metaquotes management spend a lot of time and efforts to improve MT4 and it also depends on broker builds (performance, freezes, compatibility etc.), but Hotforex MT4 builds work perfectly. I always download and update to latest software to get best performance.