I attended at San Diego last week and the conference was really great, however, one thing I dont understand is the installation. They mentioned that all SAP NetWeaver components could be installed on one server except XI. But if you installing it all on one server, is it installed on the same Database as MDOC, or is it several database instances? If you have to create several instances I assume the server will have to be rather big in terms of hardware. Of course this is not recommended in a production system, but my thinking was actually to have a common server for all NetWeaver development and one server for all QA but seperate servers for the production system. That is the reason why I actually ask the question, because if you have it one the same database instance it will be rather difficult to refresh the QA with PRD copy if you have several PRD systems.
The idea is to be able to install the whole system on one host, while this may truly not be good advice. We are working on usual scenarios and recommendations on how to install them. I don't know abotu the XI restriction but it is in notes if it applies.
I don't understand what your problem is concerning updates. At least for java you will have the updates on a JDI server that is separate anyway. And if you still have the transport for the abap system this should be the same issue - while I'm sure not an expert on all abap issues.
i think you're free to choose, wether you want to you use MCOD or not.
if you don't use it, you have to make sure that your hardware can handle multiple db-instances.
but i don't recommend using MCOD (it's my subjective opinion!). i've got a better feeling, when every instance is separated to have more possibilities in case of failures.