Judging from the examples on the Wikipedia pages, it appears that Design Strategy may well be just a new term for product/brand development, and Content Strategy a new term for the editorial process.
And in fact the Design Strategy page could do with some serious "content strategy" applied:
.. interplay between design and
business strategy, forming a systematic approach integrating
holistic-thinking, research methods used to inform business strategy
and strategic planning which provides a context for design...
Translating insights into actionable solutions ...
Continuing on my "nothing new under the sun" theme, for initial inspiration I'd recommend looking up Raymond Loewy (Wikipedia), the prolific industrial designer who managed to both cover everything from graphics to locomotives and popularised the whiole idea of products being designed at all:
Shell and former BP logos, the Greyhound bus,
the Coca-Cola bottle, the Pennsylvania Railroad GG1 and S-1
locomotives, the Lucky Strike package, Coldspot refrigerators, the
Studebaker Avanti and Champion, and the Air Force One livery.