The presentation is about RSA accumulators, the paper has been accepted
at CRYPTO 2019, and I think it can help a lot making your system scale.
A protester can batch signatures into an accumulator and commit it to a
blockchain once every X minutes (for the timing concerns) instead of
having to commit each signatures separately.
I didn't know about accumulators, thus my suprise, but if you know about
it then I guess this mail isn't of much help :).
From Pierre-Louis: