In the Marvel Universe, the mutants are a species deemed separate from humanity. But as time progressed and the incredible variances in their powers grew, several subcategories of mutants began to surface. One of these groups was a type of mutant known as the Neo. Prior to their extinction, the Neo were actually much stronger than the baseline Homo sapiens superior. As a result and due to their small numbers, it is conceivable that the Neo were the next evolutionary step for mutantkind. In fact, the manner of the Neo's extinction all but confirms this fact.
The Neo first debuted in X-Men #99 by Alan Davis, Terry Kavanagh, and Brett Booth. They were a form of Homo Sapiens Superior that elected to isolate themselves due to their greater power in comparison to the rest of the mutants. Their powers were so great that they even derisively referred to normal mutants as "spikes" a play on how the mutants barely even register on their personal power scales. The Neo would have happily remained in isolation had a tragic event not cost them many of their numbers.
The Neo were brought out of their isolation when the High Evolutionary temporarily shut off the mutant gene on a global scale. This resulted in the mutant population losing their powers, and for several members of the Neo, this proved to be fatal. Several were using their powers regularly, often in environments where they would need that edge to survive. The loss of their abilities resulted in many deaths, among them being the daughter of the Neo's leader, Domina. Enraged by the loss of life, the Neo blamed the X-Men and Mister Sinister, going to war with them for a time and gaining the attention of the rest of the world.
The Neo would remain an antagonistic force to the other mutants of the world, but things came to a head following the events of M-Day. When the Scarlet Witch depowered most mutants on Earth, the Neo were also affected. A very similar premise to what drew them out in the first place would ultimately be the means of their destruction. Eight Neo remained and traveled to Utopia, where the remaining mutant population was seeking shelter, demanding answers, not realizing that this would be their final transgression.
Utopia was under the protection of the Evolutionaries, who watched over evolution and mutants. The Neo's aggressive act pushed the Evolutionaries to wipe out the remaining Neo. But there was a bigger picture behind the extinction. To the Evolutionaries, the Neo represented a threat to the very evolution of the mutant race. They had lived in isolation with their great power for so long and yet they had not changed.
The Neo thought themselves superior to their mutant brethren because of their greater power, but the Evolutionaries saw them as the stagnation of the mutant race. If the Neo were allowed to live, they would continue to remain the same, never evolving, and by extension never becoming better.
The Evolutionaries' view of the Neo implied that the Neo were further along on the evolutionary chain than most mutants. This means that with time, mutants everywhere could achieve the same power levels as the Neo... and possibly much greater.