The enforcement of one language or dialect over others is a pretty common tool among nation-builders; the sharpest example in my mind is Parisian French taking over France [0]. Xi's CCP is definitely pretty nationalistic, so it's not surprising that they'd attempt to promote the speech patterns used around Beijing as the true form of Chinese.
It remains to be seen whether Cantonese has enough critical mass to resist being displaced by Mandarin, although Wikipedia suggests that ironically it has been prospering at the expense of smaller Southern Chinese tongues [1].
[0] https://en.wikipedia.org/wiki/Vergonha
[1] https://en.wikipedia.org/wiki/Language_shift#China