The simplest type of relationship is a good conversation with a stranger you will never meet again. Some of those relationships can have very high return on investment. The only investment may be a bit of time that very would very often be completely wasted on the phone anyway. No drama, no conflict, no potential fallout.
I agree but, are they fulfilling enough long-term to satisfy the needs? Will it be a driving force or a point of interest? It is an interesting question I think because as I see it, we need each other but if in some future we are fooled into thinking we do not, we may all live isolated in a group, none happy but none willing to make concession for others as that would mean conflict and a reduction of pleasure.
I don't think that kind of relationships can fulfill all our social needs. Not by any means. And I also agree that that scenario you present seems quite likely.