Stop of new box buying is a very big decision, even if they going to buy or sell, they will not take this too early and without any official announcement. I think there are some different reasons.
The biggest reason, I am seeing is "New Subsidiary". Recently Airtel announced separation of their DTH and other business. Now I think they are going to build a totally new subsidiary for DTH. Subsidiary means the company will have different board, CEO, Distribution etc. So Airtel maybe stopped new boxes but the new subsidiary will buy boxes and do business separately from Fiber and Telecom business of Airtel.
While Airtel(Telecom+Fiber) will not interfere in their business and also not use their DTH equipments, they will use iptv boxes for Fiber and Airfiber.
Example: Just Like Network18 is a subsidiary of Reliance but Nw18 has different CEO, Board, Financials, Distribution chain etc.