I could not find an official source that indicated that they launched with the promise of supporting rooted devices. But did find this.
Ask us anything : Official YU Response Thread - Post #5
Their current status is:
Keeping YU Updated, Always! | Page 112 | YU Official Forums
Ask us anything : Official YU Response Thread - Post #5
2. The device will not come pre rooted, but if users do root it, we will provide the same terms of warranty to them.
Their current status is:
Keeping YU Updated, Always! | Page 112 | YU Official Forums
We would like to inform you that we are not providing the support for rooting also we never recommend customer to root the device in case you root your device at that time mobile can be malfunction or PBA of the device get crashed.
Note: We are not providing the warranty for Android rooted devices