It's in reserve period and awaiting retirement. If all goes well then Tata Sky will get replacement in July or August. I think reason for activating Horizontal Polarity on GSat can only be any of the following
- Contract expiry and Tata Sky is not interested or does not find it viable to temporarily extend it.
- Insat 4A is running low on power and Tata Sky does not want to risk riding on it and later face some major dusruption
Above all GSat is a brand new satellite, increasing load on it for a limited period won't be of any worry. Whatever money they would have invested in Insat contract extension, they can easily spend much less on a much better & reliable alternative.