Until the codex is released, this is all just pie in the sky, but I've been thinking a lot about the new Eldar Autarch and what it means to my Eldar army. Go here to see the current rumour compilation that seems to be very accurate to the released info. There's a post in there about the Autarch and what he can take.
In the current edition, your HQ choices have been limited. Avatar or Farseer. In some cases, a Seer Council of farseers or an Avatar and Exarchs. But most went with the Farseer and perhaps a couple warlocks as a bodyguard so that you couls add warlocks to your guardian squads. Farseers are cool, but modeling options are limited. Unless he is mounted on a jetbike, your only choice is to equip him with a sword or a spear as everything else is too small or a psychic power.
The autarch on the other hand opens up a world of combinations. Jetbikes, warp generators, wings, multiple different weapons of various abilities... its a converter's dream. And tactically, it leaves a lot of room for experimentation.
My chaos army has a virtual host of different leaders: Daemon Prince, Terminator Lord, Sorcerer Lord, Jump Pack Lord, regular Chaos Lord, and even a Chaos Lieutenent, each one filling a different role depending on my mood that day. I think my eldar will have similar variety in that I think I will end up with a few autarch models fulfilling different roles.
Basic Autarch - For most games, this guy will have power weapon with pistol but not break the bank points-wise. Plan to attach him to an Aspect squad and ride in a wave serpent or Falcon.
Fast Autarch - Warp Spider generator, bansee mask or mandiblaster, power weapon & pistol (or maybe fusion gun)
Shooty Autarch - Reaper Launcher, fast shot power. Act like a leader and a sniper.
Supreme Commander - Jetbike, Laser Lance, mandiblaster, close combat exarch powers. I expect him to be most expensive, but the deadliest on the charge.
Wow, just thinking about the last one makes me itch for the conversion opportunity.