I think the lazer/ lightening weapon looks suspiciously similar for both units. The soulhunters ride on these scooter looking vehicles - so maybe this one just hovers and maybe works like a reaper or something. Its all a big guess though.
If I recall correctly, Diamondback's were in the alpha as well, they just never made it into multiplayer. Either that or I'm mixing them up with another unit.
Still remember watching a video where Thor's were built by SCVs.
The more I look at it the more I think it isn't a air unit. I think the hover tank thingie looks more of a possibility for harrassing and it does make sense as Protoss has already a strong airforce so they wouldn't want to double up, ie the Phoenix can pretty much harrass from the air already.
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