My first impressions of the real world examples page was that this could hardly be called modern - it looks like UI design from the 90s.
I am sure the modern part relates to the best practices and flexbox usage, but I think you may struggle to get any adoption of this without providing a really nice example page of what could be possible.
It really doesn't (look like UI design from the 90s). There is definitely something retro about it but for the web it's definitely beyond 90s. The more I looked at it the more I liked it. I wouldn't use it on a project but I wouldn't harshly judge a site or app that used it.
I think a palette shift would completely remove the retro aesthetic. They should probably do that if they want people to seriously consider using it.
I am sure the modern part relates to the best practices and flexbox usage, but I think you may struggle to get any adoption of this without providing a really nice example page of what could be possible.