Its ok to be humble, but I am not sure the argument about size holds merit. Surely, the costs are at most linear per person: the bigger state might have a higher cost, but the cost per person is unlikely to be higher. I would rather expect the opposite: some of the cost would be amortized effectively, and even more so by the fact that a preexisting system means less reinvention is needed.
The problems are thus not scale, but things specific to the nation itself. The USA, for example, is unlikely to follow a similar path any time soon due to a distrust of public works and preference for private enterprise, a (currently very well motivated) suspicion on grounds of privacy, endless political impasse, problems with procurement, bureaucratic momentum, and so on.
But inefficiencies scale up super-linearly. The USA, for instance, has less cultural cohesion and sense of national identity than Estonia (the Russian minority in Estonia being the exception that perhaps proves the rule). Additionally, larger countries necessarily have more layers of bureaucracy, which make national programs more difficult to implement (the USA still does not have a national identification card, though I think RealID is still going forward, largely because of resistance on the part of states).
In theory federalism can make up for some of the inefficiencies of larger organisations. In practice, there's a strong centralizing tendency. (As seen in eg the US and German political systems.)
Getting larger groups of people to agree on things is where scaling becomes a problem. Especially if some of the group is ideologically opposed to others in the group.
The problems are thus not scale, but things specific to the nation itself. The USA, for example, is unlikely to follow a similar path any time soon due to a distrust of public works and preference for private enterprise, a (currently very well motivated) suspicion on grounds of privacy, endless political impasse, problems with procurement, bureaucratic momentum, and so on.