-Invites after beta: After the beta event is done, will there be a bonus for invitations? A CE award, a title, costume equipment (Hearts and friendship symbols :D), or something else? Most games have them, but that doesn't mean SK should. It's something to think about though.
-Equipment Unbinding: I understand the point to binding equipment. Especially when equipment is the only real way that levels are tracked on SK... but a CE cost or a rare item could be something to do to make your old weapons worth something to someone.
-Guild Advancement: I don't know much about guilds as they are, but I haven't seen much use for them besides networking (though this is a -very- important part of SK). Maybe every member giving an allowance of their heat to the guild to level it in order to upgrade skills (attack/defense bonuses? I've seen those wolves do em) that affect other guild members. Possibly, higher level (or all, if the levels aren't a popular idea) guilds can access more difficult dungeons? Yet again... something to think about if the idea tickles your fancy.
-Player owned housing: I don't even know what to suggest here, but it's an idea that most people like. I don't see how it'd work very well or even be useful... but doesn't everyone want a place to call their own? Could be a guild hall instead, but yet again... I have no idea how it'd work.
-Large dungeon runs: 4 people parties are great. They're convenient. Yet, as I was implying with the guild dungeon thing, bigger is sometimes better.
-Party Parallels: A random occurrence where two, three, or whatever amount of parties suddenly see someone else running around in the fore/background? Flipping switches that start up spikes or flames? Backstabbing? Assisting? I think it'd be funny, but I could also see where it'd be a pain in the firm posterior to code and to suffer through when the other parties decide they like to destroy you.
-Equipment smelting: What do you do with that level 10 sword that doesn't even alchemy well? You bought it when you were just a tier one, and you worked with it so long not understand just how little heat would improve it... well, you could sell it... for 10 crowns. Why not have the ability to take some of the heat you've upgraded it with (10%, 25%, whatever) and put it in a new weapon? Destroying the old and making the new. Let's face it... some equipment isn't even worth it as a costume.
-Mountable turrets: Hopping on a one man turret to rain death on monsters while your team keeps the thing protected? Seems kinda fun...
-Vehicle: If there's ever going to be another town, then an over world run with four (one one on a central, topside turret) knights shooting off at monsters in a rail shooter style event?
-Guild emblems: Uploaded images... reportable if they're inappropriate.
-Dance emote: That actually shows them dancing.
-Pets: Vanity pets? Sounds like fun to flaunt your achievements around Haven.
-Summons: A trinket that lets you summon yourself a mech body guard once every few minutes or once per depth.
-Give me the key for once.
PvP dungeons where two teams compete to reach a boss first could be pretty fun.
I'd like to see some tricks and traps in dungeons that are designed so multiple players are required to navigate them. Eg, a set of parallel halls that two players must traverse simultaneously to trip switches and reach a treasure. Make them optional, so if the group is too small or one player dies, the other player can escape and move on to the next floor anyway.