Is smooth scrolling going to be working on 4.8 release. Its one small feature which I really want.
Yes and no. You need to understand that smooth scrolling has nothing to do with KDE. It's a feature of Qt and you have to bug Nokia about it who show no interest in improving traditional GUI elements when Qt 5 is just around the corner.
Smooth scrolling is available since quite some time in newly introduced GUI elements which Nokia added mainly out of self-interest for mobile platforms.
The interfaces of all applications would have to be rewritten almost from scratch – which is a lot to do if the only gain is slightly different scrolling behavior.
That said, newer GUIs are typically written using the more recent Qt GUI elements, like anything Plasma-related.