Alright some are taking this letter to be sort of a corner stone for Bleach, as if that’s when Kubo started writing what he really wanted to. The letter was from 2010 and Bleach didn’t experience any changes around that time, instead it only started drastically changing around 670 I think. He had 6(!!) years available to write what he wanted to and explore the story in a way he saw fit. So let’s see how he used those years.
Farewell Swords (423) was published around 11th October 2010,
Death & Strawberry 2 (459) was published around 3rd August 2011 followed by Deathberry Returns (460) on the 17th August 2011. All of these chapters HEAVILY featured IchiRuki.
The Kubo-approved “Thank You” (episode 324) aired on 4 October 2011.
The Lost (chapter 476 where Rukia expressed gratitude over his unwavering resolve and how that changed her and SS’s fate) was released on the 7th December 2011.
Death Saves The Strawberry novel was released in 12 September 2012.
The Honeymoon colorspread was part of the 2011 Bleach calendar.
We even have the latest arc (2015-2016) where numerous times it was hinted that Ichigo would stay in Soul Society (the Yuki guy was supposed to be an apprentice for Ichigo, the death of Yamamoto signified a change in leadership/mindset for the SS, and the tickets Kyoraku handed out were a hint) and that Rukia would play a bigger role (her Bankai was hinted to be shown again and Urahara’s words in 666, which was published around 16th March 2016). Just for reference Fade To Black was released in September 2009. Ichigo activated his fullbring (which to Riruka was linked with love) while thinking of Rukia, the “Speed of the World” poem, the Bonds That Never Break colorspread, etc. all happened around 2011.
Between these dates there were many other indicators of who got more development (the whole FullBringer/Lost Shinigami arc was a IR arc) and many other moments/interviews. He had 6 years to develop his “starting ideas” more and yet nothing changed around 2010-2011, if anything those years were pretty good for IchiRuki shippers. I call BS on “I intended for this to happen!!1!!1!”