This new origin doe make some sense, they should have probably made so that the chemical that The Joker "fell" into as The Red Hood was actually mixed with the Lazarus Pit, the meteorite, or the swamp that turned Solomon Grundy. This would make The Joker immortal but not extremely old as well because what would The Joker have done before Batman? Even in some origins Batman is the reason or cause that he fell into the chemical that turned Red Hood into The Joker. It would probably make more sense or be more believable if the chemical he actually fell in was somehow related to either the Lazarus Pit, the meteorite, and or the swamp. There are also multiple ways to combine the chemical in ACE chemicals that he fell into with one or even a combination of them, for instance they could have used the swamp water as a base for the chemical then infused it with extract from the meteorite or from the Lazarus Pit, although the Lazarus Pit would have been a long reach as it has been protected for hundreds of years. The most simple and believable way would be to use the meteorite and swamp water/fumes.