I've done this in two different worlds now on windows 10 and in one world they teleport to y512 and the other one all the way up at 32767. If you push a shulker into the portal and can't find it make a creative copy and run /tp @s @e[type=shulker] and it will take you to it if you only have one. If you already sent multiple through the portal name a new one and send it through and use /tp @s @e[type=shulker,name=_____] then you'll at least know where your shulkers are going
chaosnip
can confirm that this happens as described.
I've done this in two different worlds now on windows 10 and in one world they teleport to y512 and the other one all the way up at 32767. If you push a shulker into the portal and can't find it make a creative copy and run /tp @s @e[type=shulker] and it will take you to it if you only have one. If you already sent multiple through the portal name a new one and send it through and use /tp @s @e[type=shulker,name=_____] then you'll at least know where your shulkers are going