I think there are a couple of questions which can help drive your strategy...
1) Who will be using the content - and how secure does it need to be? Some repositories are better at dealing with at least some minimal security better than others. For example, I don't want to store my training materials that are used in my product knowledge base in Marketo, since the URL isn't restricted at all, vs Salesforce which allows me to put some restrictions on whether somethinc can be shared or not. Granted, nothing is really perfectly secure, since someone can easily download a pdf and then email it to someone else, but if someone has to "log in" to get a specific document, that might give them pause before sending it on to someone who doesn't have the credentials.
2) Who is producing the content - and do they have "upload" access to the repository? If the content producers don't have access to the repository where that content will be stored, then the content producers will find a different place to keep/share it, since the repository owner may become a bottleneck. For example, if you want to share technical specs in the fulfillment center and you decide that Marketo should be the repository, then you'll need to ensure that whoever "owns" the finished product can add them to Marketo (or update the existing file in Marketo) - otherwise your Marketo users will have to manage that process.
One unified repository for all content shouldn't necessarily be the end goal, rather finding the best repository for each type of content. As long as the content can be appropriately and easilty accessed by those that need it, then the number of "copies" of that content will be reduced. Copying happens when people can't find what they need, or can't share it easily. ("I'll just make a copy of this and post it to my share drive for you"). Copying also happens when internal users don't have the mindset to share the link to the content rather than the content itself. ("I'll just download the whitepaper and send it to my prospect, rather than sending my prospect a link to whitepaper")
Sorry for the long response - I hope this helps!
- Jocelyn