I benchmarked and nginx can host 30 Gbps on cold cache, on actual real world load. (I played back a log of 1 million real world requests).

So using nginx in a 1 Gbps server is definitely not asking too much of it, or I might not have understood your comment clearly.

Why would Facebook decide to use my tile server? When a company's business depends on having reliable map tiles, they either self host or have an Enterprise deal with Mapbox, etc.