I bought a GT in Jan this year - after initiating discussions and taking a drive in Dec'16. There's a thread here on it.
Anyway, in a nutshell - the GT is actually decently popular, I wouldn't know the split within the Polo range - but yeah, the sales guy (who's now coincidentally quite a good friend) mentioned that the popularity of the GT was rising over the last couple of years, especially in cities like Mumbai where the traffic has just reached insane levels. More importantly - and not surprisingly - a lot of the buyers were actually women!
Back then too and even in general - there's no discounts or offers on the GT. As far as I know - inventory allocation at the factory post production is still limited in batches and order oriented. VW usually raise their car prices in Jan - they did it during my purchase as well - but in the case of the GT - it already costs close to 11L OTR so the hike isn't likely to be too much. In my case it hardly rose by 8k i think - since I took a Jan production and made it clear to the dealer I would wait even though I paid the DP in DEC.
For me - the Carbon Steel was anyway not available in stock - white was the only one readily available at that time.
Also there isn't likely to be any major revisions to the GT over and above what it already comes with - which is quite a bit of kit. So frankly - there's nothing much for you to wait for. If you are lucky and somehow get them to give you a deal on any end of the year stock clearance - then my suggestion is just go for it now - provided you offset the effect of losing the year's worth of depreciation through a long term ownership, which is basically a target of 5+ years. Honestly, if you take their extended warranty and stuff - 5 years should be pretty hassle free period to own it before moving on anyway.
Welcome to the GT owners club!
--- edit : the GT didn't come with an armrest - so I'm not sure if you mixed up something else on T-Bhp. Unsure if they offered anything in the GT Sport which was a rather poor execution of a "special" version that VW loves to keep dishing out on the Polo/Vento range from time to time by doing some rather silly additions or tweaks. The GT sport came with a rather weird additional spoiler at the rear and some body graphics etc. iirc. Nothing much to write about. The most significant recent changes to the GT have been an upgrade in tyre/alloy size and design iirc and the new updated 330 headunit. It doesn't get anything from the Vento Highline + model (which would have been killer if they plonked the LED headlights on the GT). Then again it's VW - they'll prolly do it in a future "Special" edition and sell it for 75k+ more.
The new platform Polo launched abroad is not likely to come to India anytime soon and it is comfortably over the 4m mark as far as tax impact goes... so yeah - that combined with the entirely new platform and all the kit that's on the latest Polo - it's nogo India for now.