I know that Unreal trials will only last 1 patch each but what about the rewards?

[Seraphor]

It should be the same rewards. That's was the whole point of having these trials rotate. If they each had their own rewards then they could remain as permanent duties.
The Faux Hollows minigame is to standardise the rewards for completing the trials, under the basis that each one will be more of less the same difficulty and not able to outgear and make it trivial. Hence the harsh RNG and length of the grind. It's not meant to be obtainable by everyone within one rotation.
That's not to say they won't add to the rewards though, so people who do manage to get everything still have reason to play them, but I wouldn't expect a new mount for each rotation. Maybe a new mount each year, or when Shiva comes back around however long that takes?