OK, I've received a ton of responses to the backer stretch goal survey! It looks like the most voted for type of stretch goal is more training series:
As for what video trainings will come next, it looks like CCNA Security, CCNP, and WCNA are the winners:
CCNP and WCNA were almost tied, so I decided to put WCNA first on the stretch goal list as I feel it makes the most sense for progression. I have updated the main page with the new stretch goals and here is a copy of the current progress!
Thank you everyone!