I don't have the Sixth World Almanac, unfortunately, but a quick lookup at the Shadowrun Wiki suggests that India in the sixth world has readopted many of its more traditional habits (i.e. pre-colonial),
up to an including the old caste system. So I'd say historical tidbits such as Thuggees would be wholly fair game and entirely justified in-setting.
In terms of how you build/play them, it depends on how dangerous you want this particular branch to be. Given the
|Which are, admittedly potentially apocryphal - much of the historical information on Thuggee cults comes by way of British interpretations of Indian history during their colonial period. |
(Kali Worship, etc.) you could make the group magically awakened which would make them extremely
dangerous - the low level phansigar/noosemen would be physical adepts and the jemadar of the band could be a Blood Mage/Shaman who uses the ritual sacrifice of travellers via strangulation to cast spells without drain. I think there might even be an Hindu themed Magic Path you could canibalize in Street Magic to lay the groundwork with. And, of course blood magic opens the way for the truly nasty things (Horrors, Insect Spirts, Corrupt Totems, etc) to be brought into play as well.
You could also keep them strictly mundane: cybered assassins devoted to a particular ideology - you could even make them freedom fighters or Shadowrunner analogues in a society that has solidified upon strict caste lines. They could work as a violent analogue to some of the metahuman rights movements in the CSA.
Either way Shadowrun embraces that sort of old-meets-new juxtaposition - I mean, they still have the faux Aztec/Mayan corp-nation of Aztlan around in the canon, mass human sacrifices and all so it's not like there's no precedent for it.