Each religion has its slant on how the world works. They are mutually exclusive. Amalgamating them into a free for all just means that the different sects have meetings together...
I guess it depends on what you mean by ultimate, but even if it was a workable amalgamation that made sense, the problem with religion is its divisiveness, not its inclusiveness.
Universalism is simply another form of religion. While I've no doubt that its practitioners believe it's the best and truest of religions out there, they share that belief with the adherents of every other religion on Earth. From the viewpoint of an atheist, you're all deluded for believing in an invisible sky spirit.
Universalism is a better form of organized religion, but is not the ultimate form. It does incorporate more people into it and allow for a lot of differences in opinion and more acceptance. However all religions are flawed so there is no ultimate form. To me the ultimate form would be no organized religion.
It can be argued that Universalism, in asserting that religion is inherent, is not a religion at all, but a philosophy that shares principles with religion. Religions, as opposed to philosophies, typically involve groups gatherings, a common creed, a common belief about the origins and afterlife of mankind, and a common set of values. In essence, the term "organized religion" is redundant because organization is what constitutes religion. Universalism, on the other hand, is merely a way of conceptualizing religion and not actually a practice.
Universalism is not the ultimate form of organized religion. There is no ultimate form of religion because everybody has different believes. Religion is not perfect and the practicing of religion should be left up to everyone. Universalism is not the ultimate form of religion because there will never be an ultimate form.
Universalism is not the ultimate form of organized religion. There is no ultimate for of religion because all religion is not perfect. In order for something to be an ultimate form of something then it must be perfect. While it is close, Universalism does not take the crown of the ultimate form of religion.