The Worst Thing About Psionics in DD3E Is Its Lack of Support
The reason that Psionics should be made core is that people can then have fun with another magic system with a different flavour (point-based) to populate their campaign.
The supporting argument is that the psionic monsters (Illithid, Intellect Devourer, Gen Dragons, Gith-folks) can be well supported with rules govering their powers. Treating differing psionic creatures as if their psionic powers are independent (unrelated) SU/EX abilities is a serious patch job.
Also, if Psionics were to make 'core', then you have support for it from other classes as well. Where is the cleric domain of 'psionics' like the domain of 'magic'? How about D&Dg's support of the psionic dragon god (now online at Mind's Eye)? Let's have a neomancer which a psion could qualify for? Why not a cleric spell called "Migraine Headache" to seriously weaken psions?
What about a 'revised' magic item 'modifier' table in the DMG? How about psionics and its impact in the OA? or FR?
The way PsiHB stands now, ANY meaningful incorporation of psionics into 99.9% of campaigns requires substantial (read houserule) work on behalf of the DM. Where is the psionic items coming from? Whose updating the 'wondering monster' tables? ... etc. Of course, your DM may just let the psionic content 'slide in' with no adventure-support what-so-ever.
As far as the argument of "I don't like it, therefore it should not be incorporated." That's a weak one as well. There are far more rants against Bards on these boards ... but I've seen them played very well at tables. I've seen write-ups against ALL the core classes ... does that mean they should be 'removed' as well?
So, my hoping for them being made into core is hoping that they're better 'integrated' into the game. The current neither-here-nor-there-but-optionally-whenever-you-have-the-time-to-work-it-in-yourself approach just doesn't cut it.
That's my biggest grip about psionics. I don't mind the classes as they stand now. Everyone can find something about anything in DD3E they would have done different: and that's cool. As it stands, I've seen psions played very intelligently and it was fun to have that dimension there. However, as it stands now, psionic-support is 'neither-here-nor-there' and I rather have it somewhere meaningful instead.
It is much (much) easier for a DM to say 'XYZ not allowed' than to say "X is allowed, but give me time to work it in so that your PC isn't the only one using X in this world. Heck, the way it is now, even the creatures who use X only use it as a EX/SU with no supporting equipment."
Unfortunately, it most likely won't make it into the core revisions. But, if they did revise a few tables ... augment the spell list descriptions... add some notes here and there, it'll go a long way as well.