The content would probably scale just like everything else in the game with number of players, but you could set it to a steeper curve. That way it's technically possible with one, just extremely difficult. And extremely difficult as in makes FSC, Grinchlin and DaN look like a walk in the park.
The trick is doing it in a way that doesn't involve cramming as many enemies into as small a room as possible. Something like this would probably require new enemy types. Not that that's a bad thing.
I don't think the playerbase is large enough to support 8 player raids. The bulk of my play is in groups of two, not because it's better but because it's hard enough to locate player 2, let alone players 3, 4 and with your suggestion 5 through 8.
Maybe if it was lucrative enough? It would have to effectively out-money-make the merchants, so that they'd actually want to do it. If it was easy peasy it could also make use of the FSC farmers, but IDK.
OK OK OK I've got it! Make it super rare, like the Margrel fight but not event oriented and on the spot. So like one in a hundred clockwork tunnels during non-events have a special entrance that lets you create a party. That way you can't sell it and have to invite your friends.. and since they all want the rewards, they'll actually go on it with you.