Major changes in the new route:
Get Cojiro and Odd Mushroom in the trading quest.
The timer from odd mushroom is used for a wrong warp from the cutscene of zelda escaping hyrule castle on her horse to the nocturne of shadow cutscene. This skips about 3 minutes of cutscenes (2 minutes from the Zelda escaping cutscene, and 1 minute from the nocturne cutscene because its a 2 part cutscene and you wrong warp into the 2nd half).
Fire Temple is done as the last dungeon and used to wrong warp to Ganon's castle at the end and skip Ganondorf and the tower climb. Beating fire temple is normally a requirement for the nocturne of shadow cutscene which is why that wrong warp is so important for this route, so fire temple can be delayed.
Biggoron's sword is gotten in Adult 2.
We also use RBA a lot more, such as RBAing pocket cucco for an early wallet upgrade and cojiro for an early biggest bomb bag and early quiver, which lets us do water temple before forest temple.
You can see the whole detailed route here: https://goo.gl/2s6VAD
FAQ:
Q: Is sub 4 possible?
A: No. Not yet.
Q: Was something new found or is this just new ideas?
A: Mostly just new ideas but with the help of recently-ish found tricks. This nocturne wrong warp idea was initially proposed 3 years ago but was really bad back then. New discoveries since then, mainly equip swap, and some other route changes make this route much more viable today.
Q: How much time will this save?
A: Its looking like about a 2 minute timesave compared to the old route. More precise timings still need to be done and the route is still changing and being improved.
Q: Wasn't this route timed to be slower? What happened?
A: It was initially timed to be 13 seconds slower, then we found a timing mistake, then we found lots more optimizations and now its faster.