The first one counters the purpose of having one personal color. The color which is personal to your knight. It is personal. If someone insults your personal color you kill their family.

The second one is another punish-people-who-ditch-Krogmo-games complaint, but there have been better threads in the past which have come to decent conclusions. I would link it but someone would necro it.

Speed trinkets was just addressed and shot down. That was not the first time, either.

Shield costumes also have a giant thread regarding why they should exist.

The last one is the only "original" suggestion, though the general idea has been suggested before; when you go into a mission, only people with clearance to that mission may join you for that mission. This prevents leeching for higher missions and abuse of alternate accounts to farm.

No weapon costumes. Ever.

I must protest the lack of weapon costumes. I want to be epic and cut everyone down with Seele Schn- wait, lightsaber. I meant lightsaber. The Shocking Edge.

>.>

How the hell can you attach Dragon Wings to a mask? In addition, it would be confusing if your personal colour kept changing whenever you changed costume. People would get confused trying to spot where you'd gone in a crowd, they'd be all 'whoa who's this stranger' and I'd be like 'ninja pro skill you can't find me now' and then we'd get in a fight because I'd be a stranger intruding in their territory and things would get destroyed. That would be Bad.
I agree in a penalty for LD, but there are already people working on such suggestions, extremely recently. I have also won in teams of 2 vs 4. It just means you get extra cr for winning. Some people have legit reasons for leaving, like parents yelling to pick up the phone or the dog being sick on the couch. How would you discriminate the people with good reasons from the ditchers who leave because their team is 10 points behind?
Nick has already stated he was worried about speed bonuses becoming too overpowered. This has also been discussed extremely recently. A permanent striker bonus in Clockworks is a bad idea, as it would render some challenges redundant. Strikers with Max! MSI is a terrible idea. Recons with Max! MSI is an even worse idea.
Shield costumes... it's been suggested before, but I don't really see much of a problem with this. It would not be especially detrimental to gameplay if this was included, as far as I can think. (I can't remember what the opinion was on the original thread.)
No 5* missions for 4* players is a pretty good suggestion, since that would cut out most of the 'invite to KoA pl0x' that so often seems to litter Haven these days - oh, wait, you allowed 'by invites'. It isn't possible for lower players to enter a stranger's KoA party without invitation, and their friends or guildmates would probably be willing to invite them if asked anyway.