I’ve been searching through the threads under “Vindication of Sylvanas” and haven’t found anyone saying “she should - or will - become the Arbiter” that predates my thread yet.
I found the thread " The vindication of Sylvanas by Everien with 1,600+ comments and am currently reading through it (I have the downtime). I’ll let you know the results when I’m done.
I still think Sylvanas becoming the Arbiter is extremely stupid (and a Kerrigan Xel’naga rehash).