TL;DR: I won't update this timeline anymore.
This isn't an easy thing for me to do, given this is the longest TL I wrote in this site by far (and one that got nominated for the Turtledoves, wow!), but the more I read my own work the more I realized that I couldn't take this story to where I wanted to in a way that satisfied me, not without rewriting several major aspects of the earlier chapters like the Age of Division, the fall of the Roman Empire and the migrations of several nomadic peoples decades or centuries before they happened IOTL.
So I figured it'd be better to scrap the whole thing and start anew. I learned a lot since I began writing this TL back in December 2019, I'm fully confident in my ability to write something better now.
To the people who enjoyed this story and were hoping for a new chapter, my apologies. Thank you for all the comments you made, I'm glad I could entertain you with my writing.
I'm still very much interested in Persia, so expect a new timeline about the Sasanians or maybe even the Achaemenids to show up in the next few months.