Hm. I read this topic on the subject, seemed to be a tad hacky at the moment.
I think the expectation on the developer side might be to go the geo nodes route, since it’s already possible to put shapekeys (or deltas, which is kind of the same thing) on geo caches that way -
Not sure if this could be a way to handle shape keys in the future, since many production rigs can have thousands of shape keys making this a bit of a mess.
In any case, since custom attributes got looked at for exporting I think it might be worth looking at shape keys as well at some point.