Paper conclusion says the cost of running Vuvuzela is pretty high per month, so you would need a benevolent millionaire to make it happen.
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.