You do not want to follow each and every instance of Opportunity to get the Feeds.Instead you want an option that will allow you to follow all the instances of Opportunity.
This is not a valid requirement as the main purpose of Feeds is that the user should be able to see some relevant and important information only.
For example - On Facebook you can see the feeds only from the Pages you Follow.
You will only be able to see the Feeds for the Opportunity you follow and not the entire Business Object.
This is the expected system behavior.
KBA , SRD-CC , Cross Components , How To