We need far better indirect lighting for forward.
But TAA is extremely cursed since it would be an easy fix for the engine programmers to implement two frame/two sample hybrid post AA/TAA (no accumulation buffer were ghosting happens). This would be SO much cheaper than TSR and actually help jagged edges.
TSR looks bad in motion and cost insane. Many other engines have lightmap alternative lightings far cheaper than Lumen but Lumen will always cost the same in a static or dynamic environment.