Specifically it's advantageous because bnAB development requires 2 separate immune stimulii applied over months. Injecting protein bolus (traditional vaccines) then requires something like 6+ separate, different vaccines - so 6 synthetic paths, production lines etc.

mRNA eliminates all of that. The 2 immune pathways can be combined into 1 vaccine, and the multiple vaccines can all be produced with the same synthetic pipeline and the same distribution and administration requirements.

mRNA may make a huge difference here.

Yep. In fact mRNA vaccines are almost trivially easy to produce. I know for a fact that many biology labs around the world bought the reagents needed to make homebrew mRNA vaccines in earl 2020. Just in case big pharma screwed up. It would have only been a few days work for them to produce it for themselves and I wouldn’t be surprised if some American and European labs actually did it.

mRNA vaccines don't use regular mRNA though, they use nucleoside analogues to avoid triggering an innate immune response to the mRNA itself. is it really that easy to homebrew that? plus encapsulating it into lipid nanoparticles etc. sounds like it'd be a major project..

The lipid vesicles part is pretty simple I think. You don’t need it to last a long time, just long enough to snort it up your nose.

I am not sure about the XNAs. You might be able to get around it with increasing the dose (trivial if you are producing your own RNA) or it might be possible to use XNAs in a standard synthesis protocol. It would depend on the RNA Pol I think.