That is already Craig under Mendes and costumer designer Jany Temime. Bond's suits and apparel in general was very fashionable in Skyfall and set photos from Spectre seem to indicate a continuation of that trend. And Bond should never dress overly fashionably, he is by definition an experienced professional in his late 30s/early 40s. Men that age don't need to nor do they dress fashionably. Well-dressed men of that age have developed a personal style and know what works for them and their body types. Timeless = beyond cool, fashion = cringeworthy safari suits, bellbottoms, 90's geometric ties, and laughably skinny suits that look like they shrunk in the wash.
EDIT:
Also, I highly doubt that Highmore will fill out or grow up the way many are thinking. Child stars like Highmore are selected because they look and can play younger than they look. As a result, with the exception of Christian Bale, they also seem to grow up to be manlets (ie. short and narrow-shouldered, eg. Daniel Radcliffe, Elijah Wood, Joseph Gordon-Levitt, etc.)