Hi Raiders!
Sorry for not beeing alive on the site, But I'm back here.
If you have downloaded the last Rise of the Tomb Raider update on Steam, and if you go to the Movies folder in the game you can notice two new FMV called "Intro" and "Outro".
In this Cutscenes we can see the Croft Manor.

Crystal Dynamics, that accidentaly shows us this Cutscenes, answer us with this:

"As some eagle-eyed Rise of the Tomb Raider players have discovered, two placeholder movies were accidentally included in the latest patch. This content was not meant to be released, but now that it is we wanted to respond to the questions we’ve received as a result. The movies are part of a DLC expansion we’re exploring for Rise of the Tomb Raider. Our fans continue to enjoy Rise of the Tomb Raider and its DLC, including Cold Darkness Awakened which released on Tuesday, and we receive many requests for additional story content. We’re always listening to feedback from our fans; especially this year as we celebrate 20 years of the iconic Lara Croft and the Tomb Raider franchise together."

So, a new DLC is coming, finally showing the Croft Manor. This DLC is set after the end of the game.

The video is the following:

What do you Think?
This is not An April's Fool 
We will know more in the coming weeks!