In order to sell me, I'm going to need to see a concrete example of a psionic power that has its own game-space. One that isn't just reflavored magic. Then a class starts to be more feasible (though there's still the feat hurdle to overcome)...
Abilities that should have been unique to psionics have been flavored as magical and they have now become accepted as magical powers. This works because the powers are fundamental and wizards are a cardinal class and you can technically justify that effect through tapping into the Weave. You will probably say this is only flavor, and you would be right. But I contend that FLAVOR MATTERS! Why? Because by considering flavor we get to use our imagination to effect how the power might behave differently. This is very important to understand and is the reason I think you are missing the desire of others to have a Psionicist.
A simple illustration would be the current Monk: Disciple of the Elements. They can use Ki. Ki is not magic, it is simply "mystical energy". By using Ki, they can use powers that mimic spells so closely, that they are just given the spell to cast as told what the flavor is. I'm not a big fan of this method. Other powers they have, such as Fangs of the Fire Snake, allow the Monk to do things not described by a spell using Ki. This is fun! The Monk Shadow Step ability also allows them to mimic Misty Step, but not exactly. It behaves a little differently. So does this mean that the monk should just be considered a melee Wizard?
The flavor, that the power originates from inside the Psion and not externally, DOES MATTER and it will effect the behavior of the powers. Why does it need to be its own class and not just a set of feats? Because the Psion represents a person who has devoted their life to being the best at that ability. They are better at mental attacks than anyone else and therefore are able to do things that other people can't do just because they decided to take a feat.
******The main thing that sets psionics apart from arcane magic is the ability to augment the power.****** To change the basic way that a power behaves relative to the amount of mental energy you apply. This is vastly different than casting at a higher level. A Sorcerer comes close to this by using Metamagic, which I love, but that's not changing the behavior of the unique spell itself, just the properties of the spell casting, such as range, etc... It's a subtle but real difference.
An example? How about the spell, Crown of Madness? This is a 2nd level spell that can be cast by Wizards, Sorcerers and Warlocks. It's an Enchantment spell and does the same thing regardless of what class I use to cast it. Why? Because it is what it is. An enchantment spell that someone wrote down or memorized the words to and every time it is cast, it does the exact same thing. (That's flavor by the way) Compare that to the Psionic power, Betrayal, from 4th ed. If the power is used normally, it does basically the same thing as CoM. However, if the psion applies more mental energy in the form of Power Points, he can intensify his control over the monster and make it attack more viciously doing more damage. If he increases the amount of mental energy even more, he can further increase the amount of damage and also cause the creature to be dazed afterwards, rendering the monster useless for a round. It could be further expanded to also do psychic damage to the attacking monster. In fact, you could use your imagination to flavor all kinds of augmented changes to how the power behaves. I can envision guidelines in the Psionics Manual on how to design your own augmentations. So cool! You cannot do this with spells other than to create new spells and it's what makes Psionics unique. Those behaviors are unique to that specific power because it is not a created spell. It is mental power specifically applied and must be addressed based on the specific ability. It doesn't require components. It doesn't require a spellbook and it doesn't have to be memorized. It is simply mental energy used at varying degrees of intensity and the effect of that intensity must be defined on an individual basis.
Additionally, if you want to make a Saving Throw vs. the power, it would probably be a different type of Save. While CoM is a Wisdom save, the Psychic attacks might be an Intelligence save. Intelligence saves are fairly rare, so there is an opportunity again for Psionics to have a place.
The obvious conclusion here is that to achieve what I'm talking about with augmentations will require tons of development time in each and every Psionic power. I agree, but it doesn't have to be as bad as it sounds. It can be done by defining a few Major Sciences/Disciplines that we all know to be the archetypal psionic powers such as psychometabolism, psychokinesis, shapers, etc... Once those are defined along with some base powers, the real development and time will need to be spent in creating augmentations. This path is endless and will allow for tons of creativity and opportunity for the Psionicist to be very unique without being overpowered.