At this stage of a season, it's smoke and mirrors. To draw any conclusion from the delay, other than the team wanted more time to develop the car, is foolish. The stand out reason for me is they have 2 new very talented people in Willis and Costa, who will want to know this car inside out.
Before Costa can implement anything he needs to understand the W03. This will take time. And he started in December.

Maybe he was privy to something Ferrari were attempting, and it was possible to do the same on the merc? Maybe.
Maybe there was an intrinsic flaw he noticed, and he ordered a change? Maybe.
From the news I received a few days ago, we will see the fduct front wing. I understand scarbs has been tipped off that it will not be on the car due to it being a specific solution to a specific problem that the w03 will not have.
My question there is everyone on the grid looked at this design with great interest as there is good potential from the idea.