An appeal to novelty is the opposite of an appeal to antiquity. Appeals to novelty assume that the newness of an idea is evidence of its truth. They are thus also related to the bandwagon fallacy.
That an idea is new certainly doesn’t entail that it is true. Many recent ideas have no merit whatsoever, as history has shown; every idea, including those that we now reject as absurd beyond belief, were new at one time. Some ideas that are new now will surely go the same way.
Examples
(1) String theory is the most recent development in physics.
Therefore:
(2) String theory is true.
(1) Religion is old-fashioned; atheism is a much more recent development.
Therefore:
(2) Atheism is true.
Each of these arguments commits the appeal to novelty fallacy. The former takes the newness of string theory to be evidence that string theory is true; the latter takes the newness of atheism to be evidence that atheism is true. Merely being a new idea, of course, is no guarantee of truth. The newness of string theory and atheism alone, then, should not be taken to be evidence of the truth of these two positions.