They already stated in today's Twitch that even with a two handed weapon you'll still have a pistol. They've stated before that, that there is no switch time for the animation. Since it's instantaneous why not have the built in shuriken pistols or wrist mounted bolters in lore appropriate cases?

There will have to be loadout choices and upgrades. I would expect that the powerglove/shuriken cat combo will be one for the Scorpion Exarchs and Autarchs.
I also expect that the Exarchs will be like veterans, giving us an exp upgrade path.

Yes, in TT the Eldar can be a bit squishy. But I don't see that having to be the case here as there is no real reference to the Eldar being particularly week. In fact it is quite to the contrary. Eldar speed and skill more than make up for a lack of toughness (in comparison to marines).