Yes, Rahul Gandhi will be a challenger for Narendra Modi in 2019 and the BJP should take him seriously. If Rajiv Gandhi can become a Prime Minister overnight due to circumstances why not Rahul after spending a lot of time in politics.
If PV Narasimha Rao was made a PM and he could change the economy of the country then Rahul can also manage things with the experience of taking on the mighty Modi.
If Manmohan Singh a financial expert can become a PM and lead the country with all his silence even Rahul Gandhi can make it. He is no longer a Pappu and a challenger to the BJP especially Modi in the next elections.
Rahul has given a tough fight to Modi in Gujarat and now in Karnataka. You can see the fight of Gladiators in open for the PMs post and the Congress is buoyant with hope for the future.
Comparison of Rahul with Modi is a major achievement for the Congress. If they continue with full steam it could make some difference for the party. The way Rahul is changing shows that he would become a butterfly one day and show the Nation that he is the grand Child of Indira Gandhi and son of Rajiv Gandhi.
Now Modi could deliver and his image has taken a beating. The demonetisation and GST have brought a negative impact to his image and there was suffering of the common man due to these hasty decisions. The Congress has properly encashed them and is able to answer in the digital format blow by blow to Modi in his own language.
The so-called alternatives to the Congress and BJP may not bear any fruit and it could become a futile exercise and mar the chances of Congress finally.
So Rahul can be the Prime Minister if he can keep up the tempo and improve upon it.