Is there any plan to enable multiple critical paths in an Asana project or Portfolio?
Nothing that’s been announced. Asana doesn’t publish a roadmap so we don’t know of their future plans.
However, I moved your post to the Product Feedback forum section so that people (including you!) can vote on wanting to see this feature.
I am not sure if I understand your request correctly. From a project management perspective there can only be one critical path in a project. That’s at least how it is defined (Critical Path Calculation per PMi