While going through a portal and teleported in elytra mode, you are teleported around the same coords as when you entered the nether portal. So if you go in at x=320 z=160 instead of going into the nether at around x=40 z=20 you'd be around y=320 z=160. After leaving the portal it sends you 8x as many blocks as you 1st entered the 1st portal at (x=2560 z=1280) This process can be done as many times as possible by the game. See video for further details.
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This has already been reported as MCPE-115933, but your observations are useful so I have commented on that report (and MCPE-120431).
This also works in survival(also realms). For it to work in survival simply place cobwebs behind the portal to keep the player in elytra mode.