Yes indeed, there will be a complete turn around.
Skip to 16:35 to understand the intent and future plans of GOI regarding Alternate Fuels .
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I only see strong demand for BS6 Gasoline cars and Strong hybrids in the near future, before we go full Electric. The Electric trend will start with MSIL and Toyota (partnered with Toshiba and Denso) as the factories start more and more localization. Honda is also waiting for proper charging infrastructure in place. Japanese OEMs around world are looking at 80% charge in 10 mins. So both batteries and charging infrastructure needs to be evolved. Honda has titanium oxide battery which has a very long life and fast charging ability.
Coming to Diesels, they will be only available in bigger cars but the demand will be reduced in this decade.
Toyota, Suzuki, Porsche, FIAT has already said that they are not going to make diesel engines anymore. Because they understood that Diesel tech is becoming too expensive and does not have a market for it in future so instead they are routing their R&D money towards developing EVs. GOI will highly promote EVs, hybrids and alternate fuels. Especially Ethanol because Ethanol boosts Octane rating. Reducing sulphur content in petrol decreases Octane levels also there by reduction in caloric value or energy content of the fuel. So to boost octane levels Ethanol will be mixed with regular gasoline. The percentage of Ethanol mix is still unknown, it could be anywhere between 10-22%. I am a pure diesel car lover but my vote is for a cleaner air. BS6-Diesels have very low CO2 levels so Diesels cannot be eradicated entirely. EVs need to have a minimum of 300+ Kms range at an affordable price to be adopted soon.
How fast the new tech gets adopted is purely based on govt, financial strength and necessity of the individual and feasibility/service. Our service technicians needs to be well trained and must become proficient in handling newer technologies like hybrid and EV. Our OEMs needs to do a lot of testing in Indian Conditions to rectify any unforeseen problems. Lastly, Indian mindset ! People do not adopt it unless it fully proven.