We've known this for months. We knew it while the campaign was going on. The major new revelation is that the CIA believes Russia intervened in the US election not merely with the aim of disrupting or delegitimizing the electoral process but with the specific aim of electing Trump. But again, we already knew this. If Russian intelligence was behind the hacking of the DNC and Podesta emails, of course they were trying to elect Trump. The intelligence briefing Senators got back in September was not definitive on this point of intention. But to suggest otherwise is to believe you can intend to knock over the bottle but be agnostic on spilling the milk. Of course, they were trying to elect Trump.
In fact, I'm not sure the two purported aims are even contradictory since, as we have already seen, electing Trump is one of the most disruptive things imaginable a foreign power could do not only to the American domestic political process but to the still largely America dominated global order.
One secondary revelation of the Post story is the apparently considerable role Mitch McConnell played in blocking any effort to make a bipartisan statement about the Russian campaign prior to the election - indeed to threaten the White House that he would attack them as playing partisan politics if they did more to publicize the intelligence assessment of Russia's role in the election.
In any case, yes, this is a big deal. It's a big, big deal even if we can't say definitively that Russian interference was the cause of Trump's election, which we cannot. But the hacking campaign certainly had a major effect on the progress of election. There's no question about that.
But we knew all this months ago. Let's not pretend we didn't.