that has me beat completely. Silhouette looks 18th century, but the slung carbine doesn't. Could be wearing a tunic, with a holster or the like on the right hip, or a waistcoat and short open coat like a British light dragoon.
Heaven knows what the headdress is. It looks like a busby without a bag, or maybe a fez with a fur wrapping. Turkish WW1? Some sort of Cossack without greatcoat? Something from the Russian Civil War?
I think you are right. They could be head swapped with Esci/Waterloo Arabs or Hat Turks to give more variations. They could be used against the WWI Cossacks as well as Mespot and Palestine. The Bengal Lancers would probably be OK for WWI also to face them . The 9th Bengal Lancers for example were in Palestine.
I hope these WWI sets include a few dismounted figures like the Hat proposed Australian Light Horse.