[oooyay]

I'm also in Oregon, specifically Portland. DMARCs for fiber are largely shared by providers which is why you can have multiple providers in a given area. That way they don't take up extra pole space and the city can pay a single provider to maintain sections of line.

As long as the DMARC isn't saturated then you're only limited by the other lines also going to the DMARC and the collective activity of subscribers upstream of you between you and the central office. That's to say, you are right that it can be done but only insofar as other posters have indicated: last mile providers need to provision higher capacity lines between the DMARC and the central office.