Yes, can I do such a thing? is there a tutorial for that? Also, Can I control the activity content? for example, can I add a HTML5 canvas? or customize the activity model?
Diaspora is not a social network engine. It is an implementation of a distributed social network and has barely any reusable parts. It's just not build with that goal.
Have a look at https://www.ruby-toolbox.com/categories/social_networking for alternatives.