I’m not sure there’s anything to aim for and/or if there’s something you can do in the card (other than a switch to break the connections to the plug). The measurable power drain from USB-A and HDMI expansion cards while suspended may well be because some devices lead the hub to not power down completely. An ethernet port will likely be susceptible to that, due to support for “Wake on LAN” etc.
There’s probably a market for the card even if the power drain is measurable – hopefully Window’s hibernate does kill the card completely – but for people running Linux it’s a good data point: weighing increased suspend time (at the price of a dongle) against the convenience of a port. It’ll just allow people to make an informed choice.
If it turns out possible to change the firmware so that the board can actually power off the USB hubs on the main board upon suspend, this will probably all be moot, but as of yet, Framework hasn’t given any indication they can change the situation.
EDIT: Here is a message from @nrp that acknowledges they are aware of (at least) the HDMI issue and that they’re working on it: Linux battery life tuning - #22 by nrp