Successful multipolar/federated systems (which are republican enough for me, anyway) have existed. Like Usenet.
As a Usenet veteran, I have a tough time with the idea that Google killed Usenet. Google bought DejaNews in 2001, and Usenet was already pretty dead in 2001. Yes, some Usenet groups survived and have become effectively Google groups, but without Google I suspect they'd just be dead.
The conventional wisdom, which seems right to me, is that Eternal September killed Usenet (with the assistance of alt.binaries). It would be interesting to see an argument against this theory.
You also seem to be suggesting that Usenet died because it wasn't profitable enough. I suppose it wasn't profitable enough to carry alt.binaries. But its costs, for regular text posts, didn't seem extreme even in the 90s.
In fact, not to get all commie on you, but one of the neat things about Usenet as a digital republic was that no one owned it, and no one profited from it. The positive social value of this principle is seen in a variety of institutions. Compare to Burning Man, for instance. Who would show up for burningman.com, a subsidiary of Ticketmaster?
[1] https://en.wikipedia.org/wiki/Republic
(edit: formatting)
Federated systems work fine technically, but few have achieved widespread use. USENET was quite successful, but Google effectively took it over. (Google Groups was originally just a USENET node, but now most people are unaware that many "Google Groups" are really USENET groups, with traffic flowing in both directions, and you don't need a Google account to access them from the USENET side.[1])
If there's no place where someone can put a boot on the air hose and cut off the air supply, systems are not highly profitable. This is why federated systems are not widely successful.
[1] https://groups.google.com/forum/#!forum/comp.lang.c++