I'm kind of worried that 1200W+ is running through the traces in the board. At the same time I wonder if it's possible to push 8x Vega VII at 250W each

Bought one of these similar boards as sample today, but has a cpu socket to use a G4560 instead of the soldered 3865U. It's slightly cheaper than the onda boards and most importantly $86 USD Bitmain APW7 can be used instead of 1500w titaniums.
If on Windows..... I may share the same concerns with you... that's why putting this on Linux SMOS with tighter power controls is preferred without messing with Windows, registry, power-tables etc.
The 2400w Deltas are rated 94% platinums - I have got a bunch of these (during Parallel Miner firesales). They are really a live saver and I dont have to worry about number of cables needed even for heavy duty GPUs like 1080tis or 32 cables....