Dear Louis,
great essay, congratulations.
I have independently come up with quite a similar idea (maybe it was influenced by having read Lee Smolin's impressive book many years ago).
I felt very lonely with these thoughts and was quite glad to find somebody with quite similar considerations.
What was missing in my scenario was a reason as to why an advanced civilisation would want to create microscopic black holes.
I would like to ask you, what you think about my solution to that problem, that I try to sketch in the following (in particular if it physically makes sense to you):
The conjecture is that any advanced civilisation has the desire to do information processing.
This inevitably leads to manipulations of (physical) structures on ever smaller scales.
But there is an ultimate limit, namely the Planck scale. In a paper I found it was calculated that Moore's law can hold at best about 600 years, for then one reaches the Planck scale. (This is a time scale way shorter than the one you mention in respect to running out of energy supplies).
The point is that if we really reach this scale with information technology, we not only would be able to manipulate the very fabric of spacetime, but we could do it in a controlled way. Thus we not only could be able to create microscopic black holes, but we could create "Designer Microscopic Black Holes", seeding information into them.
The whole scenario appears not too far fetched to me, taking into account that large companies are already discussing to harness accelerators for generating synchrotron radiation for the production of microchips. Thus my predicting is that there might arise kind of a Moore's law in respect to the scaling up of accelerators to produce ever smaller information processing structures. (The idea of gamma-ray lasers might also make sense in this context).
Best regard,
Markus