I think Blackout isn't far from the truce with that image being based on the new chassis.
In the weeks leading to the presentation of a new car, the graphic and communication department of a team would be quite busy, mostly since Renault and any other teams changes livery design every year (meaning few material from past seasons can be carried over in term of communication material).
That alone would keep a graphic team busy. Social media being of importance but not so much (it's a teaser image), we can assume a minimum amount of time would be spent on the creation of said teaser.
In that case the most efficient way to produce an image would be to get a rendering of the car (or even a screen cap of the CAD software) and rapidly clean it, draw the yellow outline and be done with it (there's a reason why the image is perfectly symmetrical, it's a Photoshoped image not a pure 3d rendering).
I'd say in the midst of preparing a new season, a graphic designer shouldn't spend more than half a day, maybe a day to draw a teaser, otherwise it's a waist of time.
Rather than draw it from scratch and recreate the perspective, it would be faster to just repaint a crude model.
Yes it could be based on an older model, but the presence of the halo and the geometry of various elements on the car can lead us to believe it's something new.
Of course this is just an assumption, but as a designer myself the goal is always to propose the best quality in the shortest amount of time when the material is of reduced importance (again this is just a teaser).
We could also be wrong, but eh this is a speculation thread so why not speculate.
For the shape of the engine cover, last year Redbull already started to be more angled and flowing directly into the side of the car, it's not impossible that Renault would do the same.
Anyway we will have some answer soon.