First of all, I don't find 'networks of poll workers, local and state officials - in several states' to be all that implausible. Second, I don't think anything that coordinated or grand is required.

All you need is a few people making fake mail in ballots and sending them to be counted by people who don't have a reasonable, timely way to determine the legitimacy of every ballot.

And this is before we even touch the idea that the billionaires behind Dominion might just get some guy to put a line of code that flips every nth vote to Democrat.