Typically overland set styles become available as motifs through zone dailies or other quests. Recently there has been a delay in the case of some motifs before they start dropping from quest rewards. I expect this is to get people to grind the dailies now because they’re new and then to renew interest in grinding them again down the road for the new rewards.

Wayward Guardian in particular was datamined as a motif, so it is likely to become available at some point:

https://forums.elderscrollsonline.com/en/discussion/541400/datamine-q4-crafting-motifs-outfit-styles

Based on last year's precedent (Southern Elsweyr with the Senchal Defender and New Moon Priest styles), I'd expect we'll see them around the time we get the first DLC next year. SD and NMP came out around MArch/April timeframe, so I'd expect Wayward and Nighthollow will be coming around March/April 2021.

I'd assume Nighthollow would come from the Harrowstorm quest similar to how Greymoor comes from the WSkyrim version, but no guarantees. No clue where we'd get Wayward from though.

What I do find interesting is that the numbering for Arkthzand is so off - it's motif 96. The data collected by the UESPlog have shown that Thorn Legion and Hazardous Alchemy are 90 and 91 (which is odd, since last year Dragonguard released before Stags of Z'en and Moongrave so those numbers are in order of release), Ancestral Reach is 94 according to the logs (weird?), but there is no data for 92, 93, and 95. I wonder if Wayward/Nighthollow are supposed to have earlier numbers, but that still leaves one missing.

...now there are a lot of people in the Reach wearing Ancestral Breton, which we've heard nothing about... And this again is assuming that the motif released is the last one of the set, which is counter to everything we've seen so far...

...weird. I'm curious to see what's in store.