Hi @khurshid-alam and all Ubuntu Unity7 developers, I ran command line
sudo apt-get install unity-session
on Ubuntu Disco and it works very well. Unity desktop looks great, dash menu works very well, HUD also works, and like you said, transparent dash looks really unique now. I can confirm Unity7 performs quick (and I can feel it quicker than the built-in GNOME 3.32) on Disco Dingo at least on my hardware (Intel Pentium 4GB). It’s awesome, man. You all did good job. Thank you.