Well, for a project like this, being South Asian wouldn't be the only requirement. They would still need to do research, know how to write for RPGs, be a good editor, etc.I find this "only X is allowed to write about X" so toxic. Especially when it comes to history and mythology where only education really matters and not your place of birth and because the lines are most of the time drawn arbitarily as you can't even draw a clear line from todays countrys to history (Is someone from Tamil Nadu allowed to write about mythology from Gujarat just because both are in India (country) now even though those places are nearly a thousand miles apart and have not been in the same country for most of history, including the era you draw material from).
Representation brings three things (at least)
1. RPGs are still a very white, male, US-centric field. To some degree, this lack of representation reflects societal structures that privilege some people over others. The hobby as a whole would benefit from giving more chances and employment to people from a more diverse array of groups, and should be conscious of how it can work against structural and individual prejudice.
2. Not all knowledge is book knowledge. Lived experience adds a tremendous amount of depth, especially to creative endeavors. What's it like to walk down a street in your fantasy South Asia? Quick, what's the name of the paan seller on the street? Do the characters join the street adda to hear the latest rumors? There are certain small details that if you get 'wrong' as an author then you lose credibility among those who know.
3. Cultural sensitivity. Per my earlier example, if a South Asian setting started going on about "thugee" cults as a villain or doing other Indian Jones-S, I'm out. There are many orientalizing gestures like that that people who are not connected to a given culture tend to continually make (granted, non-minority authors could educate themselves on what sorts of tropes/imagery/etc to not use, but they seem to continually get this wrong). But there are more dimensions to this than just the US one. For example, Hindu nationalists in India have a very particular and very exclusive understanding of both religion and what "India" is or should be, and if I were making a SA setting, I would want it to be at least subtly critical of that homogenous understanding of identity. On the other hand, you don't want to offend the many (hundreds of millions) people who don't politicize their religious identity in that particular way. Finally, if you do raise the ire of said Hindu nationalists as a publisher, they will come after you hard. I've seen this happen in non-rpg contexts and it is not pretty.