I immediately have hesitation with that idea, but:
-48VDC is already a common standard in computing and telecommunications. Though, I'm not sure of the full potential consequences that would come up with an inverted polarity and higher voltage.
(negative voltage rails have been on/off 'a thing' in PCs, but have almost always been fairly low-current)
Negative voltage is not a big technical issue; but it's also unnecessary.
A variable voltage, for example 12V/24V, is also not something complex to implement. However, PSU manufacturing cost would go up because it would need to supply two voltages, one fixed 12V for the mobo and one variable for the GPU.
A side note ... 12VO for mobos doesn't seem to become mainstream anytime soon but if it ever does, everyone will suddeny discover, surprise surprise, that we actually need more volts there.
'The numbers' say that *if the current can be equally-distributed*, there's more than enough 'meat' to the connector for .6KW+. (I think that's what the standard was trying to facilitate, with the sense pins)
OTOH, Real-life (as opposed to 'on-paper') physics tells us this is a very bad idea.
IIRC, this is why it's HIGHLY DISCOURAGED to use multiple wires in 'AWG-equivalency' for both DC in cars and AC in mains wiring. Even with a de-rating, factors come up that can suddenly change resistance on one of the multiple conductors; potentially causing a cascading failure.
I don't know but it can't be just universally discouraged. PC connectors have had multiple parallel wires at least since the
IBM PC XT (main power was through three +5V and four grounds, other voltages were auxiliary).
De-rating is a thing however, and I am amazed that no one has mentioned it so far. If one contact pin and one wire can carry 12A, six of them in parallel can't carry 72A because you can't guarantee an exact, even distribution of current. So, to give an example, the capacity drops to 6 x 11A. Then there's another obvious reason for de-rating: heat density in connectors. So six pins close together can't carry 6 x 11A but only 6 x 9A if the connector is expected to operate at up to, say, 60°C ambient temperature.
Here's an example from Molex's documents for Micro-fit pins (I'm not sure if the 12+4-pin PCIe connector counts as 6-circuit or 12-circuit):
I found another interesting bit of information at Molex. They make
female pins with dimples (only two on each of the two sides, four in total!) as well as
female pins with springs on each of the four sides. The latter is marketed as RMF or Reduced Mating Force.
Available with lubricant too but let's leave that for another day. So I must assume that one type of pin is not necessarily inferior or less reliable than the other, but there's any number of details that Astron could have screwed up, such as manufacturing tolerances, the choice of materials, thickness of metal and so on.