Quote Originally Posted by Rhyfelwyr
However, we should not forget that the mode through which they are implemented (eg whether by organic cultural spread, or more forcibly by oppression) is really a separate matter entirely, yet it has been conflated constantly throughout this thread.
I'm not so sure. Viking is using the sense of "multi"-culturalism in the sense of 'sheer number of "cultures" within some defined geographical area'.

Now, whether or not monoculturalism counts as "organic" depends on whether you want to consider coercion as organic or not; anyway, clearly multiculturalism by the OP's definition is the default, and certainly "organic", state unless we're talking about scattered non-agricultural tribal groups across thousands of miles, basically similar to what Moody has pointed out.

Therefore, one versus the other will inherently draw on different, though not necessarily un-overlapping, "modes of implementation".