You're guess is almost certainly right. I was there during a brief post-signing/Q&A conversation about this topic, and Sanderson was explaining that rather than creating new OP weaves(beside what Jordan intended to add and left notes for) he would rather show the skills of the characters increasing, and the pressure of survival in the LB by making some of them think of new ways to use what they already know or to adapt "economical" weaves to use them as weapon. He gave as an example (maybe fictitious) that deathgates against Shadowspawn might could lead Asha'man to use opening gateways to impede or slice up human foes.

Brandon said that a big focus of his pre-writing re read was to catalog weaves and start imagining how some of them could become weapons, or help in warfare.

In short, it sounds like new weaves will mostly be stuff Jordan had planned for the last book and documented in the outline or notes, and creative ways to use the known weaves is by and large Brandon's own contribution.