That looks all the world like a Micro-Fit 3.0 drawing, whose contacts are normally rated at 8.5A, but here they're claiming 9.2A each. Also, the largest Micro-Fit terminal is made for 18AWG, but the article mentions 16.
I suspect what's happening is Molex is making a new version of the terminal with higher clamping force or better plating, to keep the temperature rise down at higher current, and larger wire grips, to accommodate the thicker conductor. (This will also allow more heat flow away from the contact.)
However, the contact pitch is unchanged from 3.0mm, meaning the cavities in the housing can't grow any more, so the wire insulation thickness will be limited. That's not a big deal electrically since it's only 12 volts, but it's a consideration mechanically since the wires will be less protected against abrasion, pinching, and other damage.
But that is allowing a maximum temperature rise of 30C, it uses 18AWG wire as you say, and it's supposed to be capable of 600V AC/DC; it's not supposed to decompose/leak more than 5mA when exposed to 2200V.
All of that is overkill for inside of a PC. If you're willing to limit the operating voltage to 12V and can guarantee that your board side conductors have big, multi-plane copper traces pulling heat out of the contacts to an actively cooled heat sink, you can get away with a lot that you couldn't if you were using the connector as, say, an in-line disconnect in some conduit for a 480V servo drive.
48v made sense years ago, the only reason we haven't done it is inertia. You're spot-on; the PSU is not making voltages that're directly used by components anymore, with the possible exception of 5v for USB and stuff. Everything else has a local DC-DC converter and the "12-ish" is used as an intermediate distribution standard.
Pursuant to that, the ATX12VO standard is a huge step in the right direction. It ditches the 5v and 3v3 rails from the PSU and uses 12 only. This requires only modest changes to peripherals, most of which were getting most of their power from the 12v rail already.
I think it's an excellent stepping stone on the way to an ATX48VO or something. That will require some more changes because a lot of popular power semiconductors are only rated to 30v or 35v or something, so there will be some push for a 24v compromise, but I think the efficiency gains with a higher voltage will ultimately win out.
https://www.molex.com/molex/products/family/microfit_30?pare...
I suspect what's happening is Molex is making a new version of the terminal with higher clamping force or better plating, to keep the temperature rise down at higher current, and larger wire grips, to accommodate the thicker conductor. (This will also allow more heat flow away from the contact.)
However, the contact pitch is unchanged from 3.0mm, meaning the cavities in the housing can't grow any more, so the wire insulation thickness will be limited. That's not a big deal electrically since it's only 12 volts, but it's a consideration mechanically since the wires will be less protected against abrasion, pinching, and other damage.