However, I wonder if it's starting to become a bit like "Modern" in reference to art or architecture

You mean like referencing a specific time period instead of just “recent”? Well sure… but that would be specific to which Nu-thing you’re talking about, not “Nu” itself. Even your example of “Modern” refers to entirely different time periods and time scales depending on whether you’re referring to art or architecture. 1890 was part of the “Modern art” period but “Modern architecture” is wouldn’t exist for another 40 years.

Nu-metal was popularized in the 90’s but Nu-prog wasn’t until the mid 2000’s.

And in all of these cases, the terms were coined with the term NU to mean “new” at the time they were named. Nu-metal is old now, but it was new when they named it that and is why they named it that. So whether you define “NuTrek” as post DS9 or the movies or the current batch of discovery-era shows, you’re still using “Nu” to mean new, recent, or modern, not just in its time period of release but new in that the approach to them has changed with the times.

I don’t think anyone is using “NuTrek” to specifically compare it to NuMetal.