Incorporating a new "Avatar of Cegorach" would require a revision to the lore. The Asuryani Avatar of Khaela Mensha Khaine is a fragment of the true god, that god being destroyed and his essence being scattered across the craftworlds. The avatar of Ynnead, meanwhile, remains nascent, Ynnead not fully manifesting within the material realm yet. Cegorach, meanwhile, is said to have survived the fall of the Aeldari and to have escaped into the webway. There is lore about how Cegorach will take on the guise of a member of a Harlequin troupe, and this lore is represented in the
Great Harlequin stratagem. Creating a separate model for Cegorach would contravene that lore.
There were actually numerous conversions of Harlequin Wraithlords (and other Ghost Warriors) over the years. During 1st edition, Harlequins could also take other robots and vehicles, including those of the Imperium. The problem we have now is that the lore for the Harlequins has changed. Where Aeldari Ghost Warriors are created by taking a spiritstone and having the spirit of a long dead Aeldari warrior provide the animus, the Harlequins don't use spirit stones. If
GW were to introduce some sort of Harlequin Ghost Warrior, they would have to account for the Harlequins no longer using spirit stones (there are ways to do this without being ham-fisted).
All that said, I loved the old Harlequin Wraithlord conversions and would certainly enjoy seeing that concept incorporated into the sub-faction if for no other reason than to see modern versions.
The 1st edition Harlequins pre-dated the craftworlds as we now know them and many of the original names for members of a Harlequin troupe were appropriated by the Asuryani, those original names being replaced.
- The High Avatar became the Troupe Master so that the Avatar name could be used for the Avatar of Khaine.
- The High Warlock became the Shadowseer so that the Warlock name could become the battle psykers.
- The Warlock was merged into the regular Harlequin Troupe members (see the Warlock usage above).
Personally, while there are certain elements of modern performance art as clear inspirations for the Harlequins, I don't want them to become too much like modern performing arts. That would lower them to the level of parody.
Personally, I like the concept of the Harlequins as small and nimble, a force you use to
augment a larger Aeldari force. I feel the same way about the Adeptus Custodes, too, but
GW has allowed them to become a full army instead of just being an add-on to an Imperium army, so I wouldn't be surprised if
GW ever decides to expand the Harlequin model options to allow for a viable whole army concept. I'll be disappointed, but not surprised.
With regard to Harlequins representing specific roles, we already have that to a degree in the current units. Perhaps an expanded range of stratagems might fulfill this concept (and save Harlequin players from having to buy different models).
What would be interesting would be some character models, special Troupe Masters and perhaps some other characters that might be unique to each of the Masques.