I think that Warlocks WILL be equipped with Witchblades because Warlocks are like synonymous with Witchblades in lore and Farseers seem to prefer Singing Spears more.
Question about witchblades, there are any 2 handed witchblade? in the TT rules they are 1h weapons, and I don't know of any warlock in the 40k lore with a 2h sword ( the IF captain in the first deathwatch novel by CS Goto... /facepalm) but if you look at the miniatures or some official art the witchblades are huge, even as tall as the warlock... A couple of images: This is a warlock model wielding his witchblade with 2 hands (can't post 3 images I'll post the link) here I can't find the model in the GW website, so I guess it's an older model, seems to perfect to be official.
I'm sure that there are two handed witch blades. There is an amazing level of variety in the 40k universe. Just look at Maugan Ra and his Maugetar. He had it crafted just for him. For the Eldar a weapon is a very personal, important item. They customize them extensively.
hmm as far as i know all or nearly all the CSM weaponry gear and other stuff got so far corrupted that there is something demonic inside