Following the popularity of SOA maturity models, a number of EA maturity models have started to appear.
However, if the purpose of this kind of exercise is to assess and improve the effectiveness of an Enterprise Architecture program, then I think it's more useful to think of these models as Excellence models rather than Readiness or Maturity models, and to take inspiration not just from the SEI CMMI but also from excellence models such as Baldrige and EFQM.
There are two important points about these excellence models. Firstly, they don't only look at the capabilities but also at the outcomes produced by these capabilities. And secondly, they provide a systematic framework for developing a customized capability model for a particular enterprise. We shouldn't expect people to invest in specific EA capabilities just because some EA guru thinks it's a good idea, or just because lots of other organizations have adopted this as a "best practice", but ultimately because this capability can be demonstrated to produce the desired effects in this particular enterprise. Whereas an immature organization may have to take some of this kind of thing on trust, a mature organization should be striving for EA excellence, which means that every EA activity is tied to results.
Incidentally, when I have talked to people about Adoption and Excellence models in the context of SOA (in my work with the CBDI Forum), I have perceived a little resistance to the word "excellence". Some people seem to interpret it as meaning quality for its own sake. But in Baldrige and EFQM, excellence means value-for-money, doing exactly those things that contribute to the short-term and longer-term goals of the enterprise and its customers. So perhaps we could call it a Cost-Effectiveness model instead.
So I think any EA assessment should include three vital questions. What does EA cost - not just the architects' own time but also the time of developers, users and other stakeholders in participating in EA activities and complying with EA edicts? Secondly, what added-value is EA producing for the enterprise? And thirdly, what is EA doing to monitor and control the answers to these questions?
To get good answers to these questions, we clearly shouldn't just ask the architects; interviews should involve developers, users and other stakeholders: thus we end up with a 360-degree assessment.