I kinda see that, for London, but I kind of just feel like black monks, in suede for instance, beats them out in every way. I actually think my black monks and brown suede monks are my favorite pairs of shoes, though I probably wear my chukkas the most.
In my mind monks look better than loafers unless you really want a more casual look, in which case it's jarring with black leather anyway. Just seems a bit incongruent, and besides if you want it to be casual it's not like monks don't fill that role just fine, it's casual just not "preppy" the same way (in my mind anyway). In fact I feel like loafers kind of only really make sense when it's sunnier or whatever, not in a place like London.
Also I just like all the other casual shoe options more.
Then again I also don't understand why people get loafers in shell, though I think that's more excusable because shell is a specific look that people like.