Google sites - Gamification [on hold]

I actually need to gamify (include game mechanics) in a business intranet, which is a google sites.

It means that i have to integrate some new functionality like missions, quests, leaderboards, user profile etc...

I need this to engage and motivate users to supply it with some information, documents etc...

Here is my question :

Do you think google sites is viable to implement what i need? It seems really hard to integrate Javascript and customize a google sites, i need my site to be really interactive and track a lot of user actions.

I tried gadgets and app script but they look like very poor and cannot interact with the main page of the site, right?

Thanks for your help :)