If the biggest risk of abuse is a multiboxer who logs a mining fighter only to fill a larger vessel, or for a 2nd person to jump on that miner only for those times to help out the main player, then perhaps what we also need are larger transports with faster mining rates. Yes, I know why its been the way it has all this time, I know that it was made and left this way to encourage group interactivity. So, when it does and those people using the same IP want to mine for each other, is that really a problem? If it would be ok to have a second guy jump on to fill his friend, does it really matter if someone multiboxes to fill themselves? Probably not at this point.
Just a point on irony though, you only ever see that problem with ore/gas mining. Junkers have the Salvager, and you know, you never see a smaller miner filling them up, never see them log a little miner for a fill that then disappears. Pretty much says, all mining factions need the equivalent of a Salvager, and we can pretty much ditch the need for party mining at this point. The hurtle, like the sally, comes in the price of the transport vs cargo size. The Salvager didn't kill scrap mining, or mining for non mining capable traders. Junkers still find themselves mining for non Junker customers all the time, and they take care of themselves at the same time.
Back in the day when there would be large Junker convoys to Alpha, everyone would help fill each other, and for non junker traders, someone would whip out a mining ship to speed things up. Their use would still not be completely side lined.