I'm looking to convert a relatively new web-based application with a clear domain model over to more of a CQRS style system. My new application is essentially an enhanced replacement of an older existing system.

The existing systems in my organization share a set of common databases, which are updated by an untold number of applications (developed via the Chaos Method) that exist in silos throughout the company. (As it stands, I believe that no single person in the company can identify them all.)

My question is therefore about the read model(s) for my application. Since various status changes, general user data, etc. are updated by other applications outside my control, what's the best way to handle building the read models in such a way that I can deal with outside updates, but still keep things relatively simple?

I've considered the following so far:

1. Create Views in the database for read models, that read all tables, legacy and new
2. Add triggers to existing tables to update new read model tables
3. Add some code to the database (CLR Stored proc/etc [sql server]) to update an outside datastore for read models
4. Abandon hope

What is the general consensus on how to approach this? Is it folly to think I can bring order to a legacy system without fully rewriting everything from scratch?