This was already the appeal (of the US side though). There is a fake political "supreme court" that was only created to over-rule politically sensitive cases that in theory could still be appealed to, but that is basically wasted effort with the current UK government in place according to the sources I have.

Edit: the actual process seems to be that with this successful appeal of the US side, the lower court has to redo the case again now, which likely means a few more months/years of solitary confinement for Assange in a UK prison :(