Well, just so people know, there was no bid on the one that spawned so far, the first since I checked all realms eu and us, I have a screenshot where it wasn't bid on for the first 11 hours (was like 7 p.m. and they start at 8 a.m. since it was ravencrest us) and I checked the last time (on website) at 9 p.m., it was still long, checked again at 3.30 a.m. but it was no longer shown already, unfortunately I don't play on us realms myself, so couldn't keep up once website no longer showed it, but a player who plays there, who I talked with on us forums kept checking until 3.30 a.m., when likely it was already medium and said it was still 5 mil.
So looks like blizzard went overboard with the starting bid if items end up being unsold, just like the rhinestone sunglasses, which constantly go unsold for 500k.
Personally, since I have a lot of gold but across many realms, to the point only 2 realms were good enough for brutosaur, I thought on a 20% chance for a 5 mil starting bid and 80% 20k, since all mounts start from there apart from tcg, I thought blizzard would let players bid fight in bmah, however I didn't want to risk being in trouble in case of a 5 mil bid, so I bought it without learning just before the patch, so that I could sell it back (blizzard nerfed this but only after the patch went live), and then obviously learnt it since apart from that hotfix the starting bid ended up being 5 mil.
Some people are so sure it'd end up capped that you might not believe it when I say "there's no bids", so here's my screen of ravencrest, you will convene that at the time I took it and with long remaining price, it's been in several hours (11) without bids, which should say enough about how much interest to cap it there is:
https://imgur.com/tTgkiiv
Also I will keep checking these days till I can find a brutosaur I can follow more, preferably on an eu realm I have 120s on.