It certainly sounds appealing!
But everything I shared about access to nature would be just as true if the urban core was made more dense. Replacing sfh lots with multi use buildings doesn’t affect the access to nature in any way. If anything, it would help the situation by providing more ridership and tax revenue to support transit to nature and investment in parks.
It may if it just pushes people who prefer sfhs farther outside of the urban core, thus increasing the distance between urban core and nature. Maybe if you can pass zoning laws to prevent it, but that seems like a politically uphill battle (if there's already an existing state or national park or conservation area, it's probably not at risk of becoming a subdivision, but it will be hard to keep a patchwork of farms, acreages, and privately owned timber from being parceled off to meet the demand for single family dwellings).
I got nervous towards the end of the walk because I was seemingly in the middle of nowhere - no one in sight - and I was losing the light.
If I take the train the other direction, I can walk up a mountain (actually a dormant volcano) and enjoy the park there. That tends to be a bit busier, but then again, humans are also animals that exist in naturally, and they tend to be less intrusive than other animals in parks.
And I didn’t even mention the rivers, islands, and beaches I can get to on foot or by transit. I haven’t tried visiting the buttes yet, but I know at minimum one is accessible by bike.
All of that nature is available and present in part because of an urban growth boundary that constrained the expansion of suburbs.