Whichever pretentious #$%^&* came up with the name sidereal essence deserves to be blindsided by a dictionary.
The amount of heroics you need to run to fit in these Pre-raid bis sets is beyond insane. The fact that this is all obtainable is great, but this also means this gear will be expected from people to join raids. Alt-friendliness which WoTLK is famous for is going down tbh.
You know the real problem here is that if experience from Titan Rune Alpha was anything to go by then it will be basically impossible to obtain any of that "Pre Raid" gear without raiding. During Titan Rune Alpha people demanded GS around 3,8k-4,2k (which is more or less mix of Naxx10 and 25). People already claim that minimum this time around will be close to 4,8k-5k. You'll literally have to be geared in order for most groups to consider you in those runs.