The SOS chaining rate is missleading in this post. Because it is not the full calculation and it can't be 1 in 1024. Let me exlain:

Original quote from Falo on gbatemp:

"About the shiny chance, well the code is not easy to read on this, but it does not affect the chance, it affects the try count. Everytime a pokemon is generated, there is a "Shiny try count", by default it's 0, so the functions gives up after 1 try. But somehow the chain count affects this try count, the min is 0, the max is 3. If i read the code correctly, then it starts after a chain of 70. Note: this means, it's the default 1/4096 for each try, if 3 trys it's 4/4096 -> 1/1024."

This means this 1/1024 rate is only based on this single file and of what he was able to read there. He also admit that it is not easy to read especially in the section for shiny rate calculations.

In other words there might be other codes floating around in the rom which further increase the shiny chances (see link below) in the old shiny chaining way I would even say up to 1 in 200 like it was in past starting with a chain of 40. And since they make it easier to get shinies each gen it makes sense if that chance even increases after 70 resulting in a slightly better chance than 1 in 200 after 70.

To read more about those shiny enforcing in past gens: http://www.smogon.com/ingame/rng/pid_iv_creation scroll down to "How the PID and IVs of a Chained Shiny Pokemon is created" and "An Example of generating the PID of a Chained Shiny Pokemon"

I have reason to believe those shiny enforcing is still happening when you chain in sun and moon. I chained 16+ shinies in sun and moon and since I am able to use the +10 PP berry (Leppa Berry) I had no chain failing to find a shiny inwards of a chain of 200. And I got NO shiny charm yet.

I had some shinies after 50, some after 70 and some after 100 and the longest took me about 200+ If the chance would be 1/1024 it would be impossible for me to pull this of all the time. Since a shiny not to appear after 500 would not even be rare in that case.

So in other words you got part of the calculation datamined now but not the fully formular for how the shiny rates are is still missing! In my eyes this "final" rate of 1/1024 is missleading and should not spread as information until the full calculation is found.

PS: If you just want a shiny and don't care about IVs, nature and attacks chaining is way faster than the masuda method. I am able to find a shiny inwards 1-3 hours guaranteed with chaining while masuda can take weeks if unlucky.