All of the above.

if I had to pick some, probably 5, 6, 9.

Pretty much I would agree withTravikibot.
Although...
I would sit back and watch the show, hearing out everyone's opinion.

Other games have a sort of constantly shifting meta associated with them. In Team Fortress 2, items are balanced and you end up with new setups for your characters that function in different ways. New maps can also influence which gear is 'best'. In Puzzle and Dragons new levels/cards/balance tweaks come out that behave similarly.

Optimally, you'd want to see this created in Spiral Knights as well. If something is underpowered, it gets buffed into what it needs to be or a level is created to facilitate it or both. This sort of thing forces players to branch away from the same old same old every time. Lets say we got 4 of those spinning switches that all had to be attacked at once to gain a reward. You know what can do that? Nitronome. Build a level around this mechanic, maybe make the bomb equivalent of pots and ship it... this renewal of desires is key- when your players stop desiring something, they grow board and leave.

I think more playable levels with unique ideas behind them, and additionally new tilesets would be wonderful. In the post-vanguard missions we got a bunch of new interesting things added into the game - but they exist for a single level.

What if we have crimson order bases as arcade levels with the attackable-rocket launchers and concrete-crystals making a comeback? Make the levels randomly generated and you're golden.
Add the "machine shop" levels into the arcade rotation. This is already a unique tileset that exists purely in rank and prestige missions, and are already randomized. We don't have a "special" construct level, and this would be great for that.

Expand upon the Dreams and Nightmares mission and let us venture further than the D29 clockworks terminal within the arcade.

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But outside of more randomized playable levels, creating more an unique weapon lines would be a good step. Alternatively, a gear rebalance themed around stat boosts would be super. Something like boost the damage on plain damage shard bombs, but give them a damage debuff so they do the same damage. This would allow players to stack additional damage boosts on these weapons and make them super deadly (old idea from Zeddy). Add MSI and MSD to certain weapons, such as MSI med on cutters and MSD low on iron slug.
Then, with armors, add more penalties about. Chaos would maintain damage and CTR med per piece, but receives bomb CTI: high per piece. Add Fuse Time Reduction (FTR) and Bomb Radius Increase (BRI) to bombs and slap these new values onto things. Mad bomber could receive damage and CTR, volcanic could gain CTR and FTR, and bombtastic could have damage and BRI. With these additions you could even make chaos have smaller bomb radius and longer fuses but keep the CTR still.

Basically, attempt to keep the game's meta more or less unchanged, but mess around with stat increases/decreases. This would change up the pace of the game and create new interesting ideas. Creating trade-offs for items would be great, such as swordie armor giving slight gunner debuffs, gunners getting slight bomber debuffs, and bombers getting slight swordie debuffs.

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TL;DR - I want more levels to play in, and more variety between gear so that no one weapon or armor is "best".