Given the way warlocks work and various other things, I would surmise that WotC sees a strong qualitative distinction between 1st-5th-level magic and 6th-level-plus magic. That's clearly where the restriction in the spell point rules comes from. A full caster's eventual ability to get multiple 6th- and 7th-level slots, at the very highest of levels, should probably be regarded as an extremely qualified exception to the rule as a reward for getting that far, and not to be taken as precedent without careful consideration. If we're basing power points on the spell slot system, then as with the warlock, I think a 1x restriction on 6th-level-plus slots is inevitable.
But if we're basing power points on the spell slot system, then really we should just use the spell slot system. If we're going to be switching to this new system with its heavy emphasis on flexibility, then immediately turning around to put slot-like restrictions on the system is pretty counterproductive. Instead, we should balance the 6th-plus psionic powers on the assumption that they will be used multiple times per day, rather than (as with spells) the assumption that they will not.
I can even venture a guess as to what this might look like. With psionics' historical emphasis on augmentation, it may be encouraged for more of a psion's "6th-plus powers" to actually be augmented lower-level powers than it is for a spellcaster to use higher-level slots for lower-level spells. We don't want a caster spamming wishes, but spamming really big confusions? Seems less troublesome.