In case you haven't noticed, there's not much reason to do anything other than solo now.
- Health revives are gone, so you can't do anything to support your allies beyond just hitting the things that are hitting them.
- You can't drop vials and capsules, so you can't heal your friends or give them your stuff before you leave.
- Loot is instanced, so the whole party is forced to travel on the same path or spend a bunch of time running around in empty rooms to get everything.
That last one is extra annoying; before instancing, one of the most important benefits of partying up was the ability to divide and conquer to clear "hit these switches to open the big door" sections more quickly. You can't do that now, and there's no real way to help your friends in an interesting way, so why bother? A four-player party is now effectively a solo party with double monster HP and 3 NPC knights. More than that, this change betrays Spiral Knights' essential purpose. Nick, if you're reading this (and I hope you do), go ahead and click on that "About" button at the top of the screen and look toward the right edge of your browser window. Go on, I'll wait. ... Back yet? Notice the words "Co-operative Exploration" on the list of features? That's what Spiral Knights is supposed to be about. And you're killing it.
Much like the Forge, the change to instanced loot was most likely intended to stop people joining FSC parties and such and sitting down, only moving forward to activate party buttons once all opposition has been cleared, a phenomenon I have dubbed "alt-dragging". Also much like the Forge, it derails the game for everyone, including law-abiding knights who actually work for their gear.
Here's my simple solution for alt-dragging: don't give loot to knights who aren't active or are running multiple instances of the game on the same PC. It's worked spectacularly for TF2, after all. I'm torn on whether to pause loot acquisition for inactive knights or strip them of their earnings for that floor; feedback on this would be especially welcome. We can keep the new system's one benefit (no drama over randomly-distributed materials) by making materials and rarities picked up by one player count for all players in the party.
As for the new revive system and no item dropping, I'm baffled. I guess removing health revives was to avoid revival being too cheap with Sparks of Life dropping every 5 treasure boxes on Elite, but I can't interpret removing vial dropping as anything but a middle finger toward cooperation. Not much to say here, just reduce the drop rate for Sparks, bring back health revives,, remove the emergency revive since it was apparently intended to fill the role of health reviving, and make vials and capsules droppable again.
Not bothering with a TL;DR this time since this post turned out so short.
Don't you know? Teamwork is more trouble than it's worth now since you can't help your party members in any meaningful way beyond hacking at monsters that they also happen to be hacking at. You can't even split up effectively now that loot is instanced.
-Round-Shinigami
On the contrary, I pay far more attention to my party's wellbeing with Seraphynx than I ever did before the update. If someone starts dipping below half health I'll look for the next opportunity to use Heart Attack. If a teammate is in critical condition and has already burnt their emergency revive, I'll stick by them and throw up a bubble if things get hairy.
-Orbwanter
To your method of preventing alts, alts can be run on multiple computers or VMs. Additionally, now you have to define what counts as "doing something". Players can simply put a rock on an arrow key, or program an auto-clicker to swing the sword.