I think that is also what the documentation describes; it was made for internal teams that were already on the DIY track anyway and the intent is to make it a .NET-nail (for when all you have is a .NET hammer).
The downsides are (to me) somewhat obvious, there is no mindshare, no automation and no decades of experience. That can also be an upside since looking for documentation or examples will not result in old-outdated stuff since it hasn't been available that long.
Yep, I've been on teams where asking for approval to run your own proxy was out of the question, but "adding an extra module to the pipeline" was practically a rubber-stamp approval.
It’s new, give it some time
While it's better than other in-house alternatives, it's not better for the entire ecosystem as a whole. The need for hyperlocal reverse proxies is a problem on its own, generally only solved this way due to organisational dysfunction or a very niche requirement.
If you're a .NET shop, it seems very useful to have a reasonably fast toolkit for deploying specialized proxies. It's still early days, but I'd expect this to become as fast as anything written in Go or on the JVM, which seems sufficient for many use cases.
It's not meant to compete speed-wise with other off-the-shell reverse proxies.
It is to me as well, but these fights are quite pervasive in our industry. It is especially problematic in the enterprise space. This is to the point as a C# dev, that I'm happy this exists, so that I have the facilities it provides, when more mature solutions are unavailable.
If I can't inspect what critical elements in my request pipeline are doing I don't want them. This even applies when we get Big-IP/F5 buying nginx and putting that inside the name-brand boxes, it's still too opaque to be useful for me.
Going further, it can be customized from .NET and shipped as part of the app which may be using nginx for some proxy features.