Some really nice advice on this thread. I don't think I have much to add, to be honest. Basic stealth tactics: Pick a spot and stay there until you get the jump on your opponent. Try to position yourself so you can attack from where you are without having to move (that's not always possible depending on the map). Once you've killed someone from your hiding spot (especially against Guilds (they will all have a tag, like 'xxxx - ' at the start of their names)) find a new hiding spot from which to attack. You don't want the next guy entering the room to know where you are without looking. Bear in mind if you are in cover against a wall and attack, you will attack in the direction your camera is facing. This allows you to bounce out on oncoming attackers and get a hit on them before they're expecting anything. Alternatively, with practice and good timing (and not crappy latency) you can use the same technique to lodge a Heavy Attack in your opponent's back as they move past. To do this one you need to not use lock-on until after you've swung your weapon. <Beware> If you use that technique, you better be sure your opponent is alone. If they're not, wait for the last person to enter the room and strike at them. You're far less likely to be targeted by those already in the room than by enemies filing in behind their comrade.
I find scorpions still have their roll, but you're right. Slipping in unnoticed is almost impossible. What I used to do is just crouch and wait by a doorway and wait. When enemy melee moved on, or when my team made a push and they all focused fire towards them, I would sneak in and start downing heavy supports. I could usually take out 2 before I got downed, or had to run away. Best thing to do at any point capture is just rush in there in groups of you can. If you're whole team goes half melee and half ranged and run in, the enemy struggles to push off 15-20 guys. Depends on how set up they are, but trading fire in doorways takes too long. Especially if they have a splash damage weapon like a plasma gun. During hold the line defense I used to wrack up 25 kills and first place with a reaper launcher, just shooting down Tranports and guys hanging out in doorways. So rushing in with melee does have its value, although with the new patch this is borderline suicidal for most classes. So Scorps still have their part to play I think.
Had a few games with scorpion this morning. Had no trouble getting top of melee kills. I can fairly reliably semi-compete with ranged players. Can usually get moderately close to the number of kills they do. I've had most success with lashsword, +2 stamina, improved aspect armor and smart pistol. The 4 stamina build is really important for me. I can not see myself doing well without that much stamina on an Eldar melee class. So far I've not really found that there's a need for too much "strategy"... just general melee gameplay know-how and experience. Quickly getting a feel for the behavioral habits of your melee targets is what nets you kills. The faster you can notice a habit, the faser you can exploit it. Newer players are always the easiest to net kills from because they tend to religiously stick to a single habit over and over. In a room full of people i tend to stay very much on the move. No more than a couple of swings at a time, and use defensive bash extremely sparingly (it makes you stand still for way too long) in cases where the other guy is spamming fast attacks and you know you have a second or two before any other enemies can re-aim at you. I don't really move around in stealth. I use it for juking and tricking (like running away behind a wall and hitting crouch) or entering an extremely busy room. Stealth is pointless if you are moving along some commonly-tread pathway, because someone is bound to be looking down their sights at you.
You can manage with 3 Stamina, but you need to be willing to use the Eldar footspeed to run from 1v3s.
