I have a follow-up u/s Friday to find out whether the placenta previa has moved at all.
Wish me luck.
update: to make a very long story short, when they started the u/s it still looked like a full previa. But when they switched to trans-vag they saw that the edge is actually 0.7cm from my cervix! We're not in the clear yet, they require 2cm clearance for vaginal delivery, but it is progress. I go back at 32w (and 36w if needed) to check again.