This is awesome!! The current recommendation of filling vias with ink is a bit finicky for my liking as well, so a simpler process would be great.
It's also a really strange coincidence - I just tested out a similar process a few days ago, after stumbling on the same MIT link. The only difference is the rivets used, and that I inserted rivets at the end rather than at the start (like @RoySalisbury suggested) . Here's a double-sided Hello World design I threw together to test it out:
(excuse the messy soldering job, I used the opportunity to observe soldering under a microscope at different temperatures - two birds, one stone, etc.)
This one uses 0.4mm ID / 0.6mm OD rivets that were used in their project, and the recommended center punch from Mcmaster as well. I found that the hole should be 0.05 - 0.1mm larger than the OD of the rivet for a snug fit, which lines up pretty well with your results!
Have you tried the ink-filling method for vias, and if so, how does your experience compare? Personally I find rivets to be a much smoother process, and the benefit of plated through holes is a huge bonus.
The rivets I got were they're pretty inexpensive at about $0.06 ea from a US Distributor, but the downside is you need to buy in quantities of 1000 per size... I'm following up with the rivet manufacturer in Germany to see about bulk pricing, so we can down-pack into more reasonable quantities. If there's a consensus on the topic, and you have some suggestions about reasonable quantities for a rivet kit, we can look into putting them up on the Voltera store!