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while watching the Q&A Cast, the outfit was mentioned several times as being available upon release of the skill. Since this will be the only buff in the skill for 6 months, the value is high. Creating demand is the first rule in marketing so this is set up to be the perfect item for a TH promo. How soon we see it there is the only question.

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over 4 years ago - /u/JagexRowley - Direct link

As one of the developers working on Archaeology, the skill and elite outfits are planned to be exclusively earned via training the skill (that's how we've designed and already developed them), and accounted for it in the skill's balancing.

Obviously, I can't predict the future (and have even less control over it), but I can't see anyone wanting to add it to TH even at a later date. TH has not broken any previous new skill embargo, so precedent should suggest this one will hold firm and, by the time it is up, a fair proportion of players will already have one, if not both, of the outfits, so any market for it on TH would be severely limited anyway.