I believe that 'metamodernism' is not the end state. The modern period, beginning in the early 1600's with the enlightenment, through romanticism, on to modernism and then to post-modernism, has each phase with a shorter time span. This is a function of the recognition of the more recent 'stages' being more identifiable. The recent is more specular, sharply in focus and finely grained. Soon, I predict, a fresher, more unique moniker will appear that is freed of need to be historically referenced.
This is not to say that metamodernism's ideas are fleeting. They are not. The reversal of post-modernism's plunge into meaninglessness and metamodernism's rejection of a claim that nihilism can be nothing but a looking down into the abyss, is profound and will be lasting. Metamodernism's insight that the post-modern dejection that results from profound lack of reason and purpose, can be turned against itself. If there is no reason to be hopeful, then there is also no reason not to be hopeful. Perhaps Keirkegaard was even more right than we supposed. Indeed, we can choose to be down in the mouth because there is no real reason to be optimistic or we can choose to see a bright future for equally little reason.
Justification be damned, then. It's one's outlook in life that counts, it is what one chooses. 'Justification be damned' does not mean that reason becomes invalid. The Logical form still caries weight but only as a tool toward an end. Reason, as the post-modern storyline would have it, does not go to the bottom. Ultimately, reason ceases to be relevant and truth, then, becomes relativised. To what? To 'the good'.
Therefore, I say, metamodernism is a transitional term. It points to a future where the good is redifined in terms of depth and universality, not just in terms of utilitarian gain. It will be redifined communally. It will be redifined by consensus... with honesty... and with sincerity.
We have nothing to lose but the chains of dispondency. Look up, not down. Look forward to a better tomorrow, not to the reenstatement of an old king, but to a newer depth and a greater height.