Americana already renders place=city, town, and village, but lacks urban districts/neighborhoods, usually tagged as place=suburb, quarter, and neighbourhood. These named areas are usually part of a larger city or town rather than being their own distinct places, but they are nonetheless important for wayfinding and orientation in urban regions.

Per the wiki, each tag represents a distinct size/importance of the area, with suburb > quarter > neighbourhood (note: place=suburb, a major district of a city, is distinct from the American English definition of "suburb", which is typically a distinct municipality in the area surrounding a city). In my experience, in US usage the distinction between each tag is only loosely followed and convention is highly variable from city to city. Therefore, I suspect rendering all three tags similarly but with slight differences will be the best approach.

In my mind, a typical treatment of neighborhoods on US city maps would be all-caps labels and/or a light font color, typically to make neighborhood labels less prominent than other labels. We'd have to make sure any choices sufficiently distinguish these places from labels for roads and independent places: I think the all-caps would accomplish this (we currently use an all-caps treatment for state labels, but I don't think the risk of confusion is too high). I think just a label without an icon makes sense given the inherent area nature of neighborhoods, and would further distinguish them from independent places which get a dot.

Here's an example from a AAA map I have. In this one, the neighborhoods are in light blue. Other samples welcome!

There are also other urban place tags: place=borough appears to be used essentially only in Pennsylvania by an import to represent a local administrative classification. It's probably a tagging error, so that should probably not be rendered. Smaller divisions, such as city_block and plot, are very rare in the US. So I don't think Americana needs to render them at this time.