On existing old world types the end portal works, i have not testes this on newly generated old type worlds due to the terrain never loading
Also in the end of an old type world the chunks have the same problem as newly generated old type worlds
Maybe this isnt a bug and its intended
Maybe the developers are making 1000x1000 old type worlds that generate with strongholds
Like they buffed the enchanted golden apple and hunger system, which could hint at 1.9 pvp
To quote what im assumning is an official source due to being on news.xbox.com "There are other features we are planning on bringing to the Ender Update as well, but we're keeping those a secret for now!"