I have also been researching the same. I am based in Hong Kong and fly Cathay a lot. However, it seems easier to maintain emerald on Qatar PC than Cathay.

However, there is a requirement to have at least 20% of Qpoints from flights marketed or operated by Qatar (or you fly 4 segments on Qatar a year).

Does anyone know if I fly a Cathay flight to Singapore from HK which has a Qatar codeshare, does that make it a flight “marketed” by Qatar? Or do I have to book the ticket through Qatar?

Thanks.