This is a question I think we should be able to answer, but information is sparse and scattered at the moment.
As @Clone mentioned, the Pro model of Glowforge has a cut area of 12x20", so with that you should be able to do objects 20" wide by ∞" long. So, 36x20" should be quite doable with a Pro Glowforge.
Many machines have a bed that’s larger than the cut area, so it’s possible that there will actually be some extra room for larger material. For instance my non-Glowforge laser cutter, which has a cut area of 12x24", has a little extra room on each side (about 2" on the left and right, about 1" in the back, and about 0.5" in the front). Larger material, maybe up to 13.5x27.5", could be shoehorned into if it was absolutely necessary. Maybe there’s a similar amount of extra room in the Glowforge… we may not know for certain until Glowforges start being delivered.