Either Cubicle 7 or Modiphius.
This will be a hard sell as the first inclination of a publisher with a new edition is to redo all the core stuff.
Although the trend right now is nostalgia, and Cubicle 7 is a British company. Just like 5e D&D was a reversion back to prior editions of the game I could see a new edition of WHFRP reverting back to something more like a mix of 1st and 2nd edition to try to get the folks who checked out for FFG's 3rd edition back on board. It would follow current trends to take those 2nd edition rules, trim then down and modernize them even more, and then release it with an art design that evokes the first edition of the game to entice skeptics to pick it up.
Btw, could C7 run this as a kickstarter? Probably unlikely... but it could be really great for fans to be closer to the project. I also think this would make a better final product.
I know that GW don't usually let their licensees use KS.
Could they make OGL Warhammer D&D, or would that be a step too far?