At most one Titan would be reprinted. More likely well see a bunch of new titans that aren't particularly impressive. I see them as being one of the big 'monster' creatures. (in the high CMC sense, not the powerful sense).
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Cyme we inne frið, fram the grip of deaþ to lif inne ðis smylte land.
The ''Titan'' cycle does not feel Greek/Roman themed at all, so I see 0% chance for this. They are just some very large giants who happen to have brokenly good cards.
The Titans, according to roman mythology, are something akin to gods, and at least rival the established gods in power. They would be more near the Eldrazi (and they have a bit of that flavour, according to the movies Clash and Wrath of the Titans, which influenced the public perception about what titans should be a lot, and that is what matters to WotC) in terms of flavour.
However, looking at the set names, it seems that it is more of a personal story. ''Born of the Gods'' implies that it is about relatable characters that are ''born'' and have some special powers due to their heritage. ''Journey into Nyx'' even more implies that this is about a personal story, or quest.
I think it would be really nice if they use this to really develop a certain character throughout the block, giving him a legendary creature in Theros, then referencing him a lot and eventually making him a planeswalker in Nyx. It would also be nice to have some sort of command structure on this plane, where a group of planeswalkers pose as gods to the people who cannot fathom where else their powers come from. They'd have to be pretty powerful planeswalkers, but I don't mind upping their power level a bit in the story. No more shall a Planeswalker be defeated by a petty phyrexian beast.