Pretty please.

    [&]<std::size_t... I>(std::index_sequence<I...>) {
      (SetupInput<I>(options, transport_manager, subscriber_queues[I], thread_pool, templated_topic_to_runtime_topic),
       ...);
    }(std::make_index_sequence<INPUT_COUNT>());

would be a lot more readible as

    for constexpr( size_t I = 0; I < INPUT_COUNT; I++ )
      SetupInput<I>(options, transport_manager, subscriber_queues[I], thread_pool, templated_topic_to_runtime_topic);
    }

Yes, there's some syntax snags around it (right now I looks mutable, something like `for (constexpr size_t I : INPUT_COUNT)` might be better), but there has to be some sane middleground.