It looks like more or less Babu is looking at the Congress from the back door. The way he encouraged Rahul and talked to Sonia with all smiles shows that he was leaning towards the Congress party. He said that TDP would play an active role in trouncing the BJP at the centre in 2019.
He never said that he would support an anti-congress and anti-BJP government at the centre. While KCR is talking about the Anti-BJP and Anti Congress at the centre, Babu is just talking about the anti-BJP government. Babu is for taking the Congress support also to trounce the BJP in 2019. That is the reason they are campaigning that voting to YSRC in AP is nothing but voting for the BJP.
We do not know if there will be a single front or two fronts at the centre. But Babu is leaning towards the Congress against the BJP.
Maybe even KCR could also be convinced for a single front in the end to trounce the BJP. But as of now, KCR is against the rule of the Congress and also the BJP. Majority of the parties want the support of the Congress and few of them do not want Congress and also BJP at the centre.