Gustaf,
I agree callbacks are an implementation technique - I was talking in terms of callbacks because their use was predetermined in Malte's proposal. If you would like to abstract my suggestions you should simply read it and replace each instance of the word 'callback' with the words 'message handler'.
The discussion of 'service contracts vs. callbacks vs. object request brokers vs. xotcl' is an escalation to a much more general problem and probably won't help Malte very much in a practical or short term sense.
I notice that the document you linked presupposes an object oriented methodology - whilst object orientation has a lot of popular support in the community I don't believe there have been any concrete proposals of how to map the functionality of OpenACS to an object oriented design. Nor have there been any discussions of how we might resource such a conversion or what timescales we might aim for. I think it is unreasonable to prevent Malte from introducing a very useful capability because we haven't decided whether to switch the whole of OpenACS to an object-oriented paradigm.
