Hanson mentions it in the original Great Filter piece, and I've seen it discussed elsewhere on the internet in internet fora (for example, r/futurology on Reddit).

It's true he discusses dark matter. He doesn't mention reversible computing or the Landauer limit though, although to be fair when he wrote that article reversible computing was relatively unknown.

I'm now realizing that my use of the term 'dark matter' is unfortunate because it typically means an exotic form of matter, whereas I am talking about dark regular baryonic matter.

If the material in question is conventional baryonic matter then it cannot be a large fraction of actual dark matter, so it loses the appeal of being an explanation for that (and yes, the other explanations for the Filter don't explain dark matter, but versions of this at one point had this as their main selling point).

The dark energy/matter problem in cosmology is still very mysterious. The current main solutions call for new forms of exotic matter/energy, and many of the detection experiments have generated null/wierd results. There's alot going there in cosmology and it will take a while to sort out.

Also, there was some new research just recently showing that type Ia supernovae are more diverse than originally thought, which is causing a rethink of the rate of expansion, and thus the whole dark energy issue - as the supernova measurements were used as distance beacons.

Now regardless of what is going on with dark energy and non-baryonic dark matter. the issue of dark vs light baryonic matter is separate, and the recent evidence indicates a favorable high ratio of extrasolar dark baryonic planemos in the form of nomads.

The actual mass ratios for dark vs light baryonic matter are also unimportant for this model in the sense that what really matters is the fraction of metallic mass - most of the matter is hydrogen/helium and such that is probably not as useful for computation.

Moreover, it isn't at all clear how you would have multiple such objects communicate with each other.

? The planck satellite maintained a 0.1K temperature for some key components and we had no issues communicating with it. External communication with a reversible computer doesn't even require energy expenditure in theory, but it probably does in practice, but the expenditures for communication can be tiny - especially given enormous computational resources for compression.

A few months ago, I asked you here what you thought the form of these dark matter entities were and you didn't reply. It seems that since then you've thought a lot more about this.

I have written about this before (on my blog) - I didn't reply back then because I was busy and didn't have much time for LW or thinking about aliens ;)