What about Vuvuzela? Haven't thoroughly examined it, but it focuses on metadata-privary and -relative- scalability.
web: https://vuvuzela.io/
repo: https://github.com/davidlazar/vuvuzela
web: https://vuvuzela.io/
repo: https://github.com/davidlazar/vuvuzela
As for signal what every prosecutor wants is metadata to show the court that user A was in communication with user B. The actual contents of the messages aren't important especially in a conspiracy case and user B is an informant, their word against yours plus metadata showing you communicating is good enough.
Besides forcing Signal to keep this metadata in the future, I wonder if they can just obtain it themselves by watching all traffic on their federated servers and timing it to discover communication networks.
It's really easy to underestimate how big of a ripoff EC2 bandwidth pricing is.
Is this 1 gigabit of accumulated traffic, or sustained bandwidth guaranteed for an entire month?
1 TiB of accumulated bandwidth at DigitalOcean costs me $5/month. I am unaware of what sustained rates are given that tier of pricing, however.
On the expensive end you'd be looking at around $600 for such at $NOT_AMAZON, and on the cheap end you'd get it for "free" because a plenty of hosts have excess bandwidth.
DO doesn't separately charge for BW or enforce any limitations AFAIK.