In form it approximates a classic "park" more than the sort of national parks you and I probably think of. I like the idea of diversity in our national parks and public lands. Some could focus on history and education, others on naturalism and ecology, others could mix and match as needed. Urban national parks seem like a fine idea and a way to encourage urban populations to explore more public lands outside of their cities too, eventually. To build a nation of parks and gardens would be laudable.

We have National Monuments and National Historic Sites/Parks for "this isn't nature but should still be a site maintained by the Federal Government".