In developing the monster section of the Basic Psionics Handbook, Welbo and I spent a lot of time thinking through which creatures would and would not be including in the monster section. There were a few factors that drove us in this regard:
1. All of the classic "iconic" psionic creatures must be included (and those that aren't OGL'ed must have the serial numbers filed off).
2. The opportunity should be seized to expand the influences of the area spanning the Middle to Far East.
3. Anything new that was added should feel consistent with Moldvay/Cook/Marsh.
ICONIC PSIONIC CREATURES
Though we have settled on the names "astral gith" and "limbo gith" for... well, the gith-you-know-whats, Welbo and I are still reworking a couple of the other names (e.g., last night it occurred to me it would be cool to nickname the tentacle-mouth thing we all know and love as the "thid", but no group editorial decision has approved this yet). Many others are already OGL (aboleth, brain mole, intellect devourer, neothelid, et al.), so it was just a matter of converting it while making sure it fell in line with the new system and the overall vibe of BX.
EXPANDING THE EASTERN INFLUENCE
We've done this both with iconic creatures and the addition of new ones. For example, the baku was re-imagined less as the elephantine creature with mixed psionic abilities, and made more like a wooly tapir that devours dreams (owing to its Chinese roots). There's also the addition of the aqlghoul, a Persian inspired ghul, that not only possesses the undead immunities, but is psionically immune as well (even though it can use psionic abilities).
If you've been following the development of this project for a while, then you're likely familiar with the story of the psionic rhino. This is likely the most BX of the creatures in the book (and why shouldn't it be, I worked directly with Steve Marsh develop the final entry). The section also sees the addition of a few more low level psionic creatures as well (including the albino toadstool and the hive-mite, as well as a conversion of the dromite—a humanoid race that feels very BX to me, even though it wasn't introduced until 3.5e). I've also created a psionic human-headed spider, the nightspinner. How has there been no iconic psionic spider before now? (BTW, this creature is going to be one of several bridges to the material I am developing for a tentative Basic Atlas of the Planes, which likely won't be finished until late next year).
Okay, to wrap this up, the illustrations are progressing, and I have only 5 spot illustrations left for the monster section, then about a dozen or so more to finish out the book. We could see the release of this by mid-October (fingers crossed).