Being the big WC3 fanboy I am, I really suggest Valve consider hiring Justin Gross or (Patrick Seitz, to an extent) for the voice of Abaddon.
I admittedly did not play much dota back in the days, but I did played a lot of WC3 and Arthas voice has been permanently burned into my brain through the campaigns in WC3.

It would also be great for Valve to ponder on the idea for a hero voice pack (just like the announcer packs) so one could switch the responses for a specific hero
I personally would love to see a Lich voice pack from the voice actor of Kel'Thuzard in WC3, or perhaps a Chaos Knight voice pack which was voiced by the Chaos space marines in the DOW1 games (NOT DOW2 and Spacemarines)