How are Rx, Tx, and ATN spec'd?
Rx and Tx are tied to P31/P30. ATN is tied to RTS of the FT230X which feeds the reset circuit for the propeller.

How are you doing the voltage translation on the Stamp I/O pins?
High speed bidirectional level translators, TXS0108E, tested to 60Mhz. The Prop Servo controller uses TXB series parts which are different in regards to architecture, which create limitations as you mention. TXB parts use a weak buffer with one-shot circuitry whereas the TXS parts use FET-based architectures that utilize an N-channel pass-gate transistor. From TI's docs: "The combination of an N-channel pass FET, integrated 10-kΩ pull-up resistors, and edge-rate acceleration circuits makes the TXS type translators ideal for interfacing devices or systems operating at disparate voltage levels while also allowing for simple interfacing with open-drain (O.D.) as is required in I2C, 1-wire, and MMC-card interface applications."

My bias is to always use a 64K EEPROM and perhaps offer a 128K one as an option.
The prototypes have a 32k, and a 64k is an option to pursue. Due to size constraints of the PCB footprint, there are limitations to the package that can be used. SDA/SCL is brought out so you can easily add secondary EEPROMs and use the onboard EEPROM for a bootloader.

Any discussion with Parallax about a PBasic interpreter for the Propeller?
Bean's PropBASIC would be one target platform for this module to allow BASIC Stamp users a very quick migration. No plans to create another interpreter.

I've seen a couple carrier boards that a had a stable 5V supply on board and would feed in a regulated 5V on the VOUT pin of the Stamp to power the module. Do you have a setting to accommodate that?
Parallax's BS2 carrier, super carrier, and BOEs tie the onboard 5v regulator output to the BS2 module 5v regulator output. Our design intent was to use this module for all power needs and incoming power should be supplied at the Vin pin. (or the USB connector which supplies Vin) The "5v out pin" is an output and should not be used as an input. You can supply 3.3v to the module and it will function, however, without 5v on VccB of the translators, P0-P15 usage is undetermined (but I can test this and update this answer).

Can you please list what advantages / improvements this has over the existing Spin Stamp ?
Key items are: 2.5-12v input range, 5v I/O, 5v and 3.3v switching supplies for efficiency and higher current, all 32 I/Os available, USB programming (no prop plug required)

Will it be possible to feed 3.3V in via the 3.3V terminal in order to have a really low power SLEEP mode and backup? That is usually possible with a SEPIC buck boost.
The enable pin of the buck boost 5v switcher is brought out to the 50 mil header to effectively shutdown 5v, 3.3v, and the FTDI. Also, if Vin is less than 1.8V the 5V switcher goes into shutdown mode and will pull a maximum of 2uA. This will also disable the FTDI chip further lowering the current draw of the module. We’ve configured the 5V switcher to operate in power save mode so even with a current draw of 1mA the efficiency is over 80% in most cases. You can supply 3.3v to the module and it will function, however, without 5v on VccB of the translators, P0-P15 usage is undetermined (but I can test this and update this answer).

Regarding the SMD power inductor behind the Prop did you test it at elevated loads/temperatures and Crystal values. Will it need a limit on crystal/pll range ?
This has been tested and no issues have been found, including during VGA generation. Note that this is a 4 layer board with full ground and power planes.

What is the target price point?
The target has been to have the full module pricing at a point to place it by or under the BS2. We will be able to meet that target, but we are still resolving some pricing on a few parts to know exactly where it will be. A base version without headers should have a price point of $35. Full version that includes headers will be above that at an amount to cover the part cost. We will need confidence in roughly 70 orders to start production.

Why does it have Micro USB rather than Mini USB?

There are two main reasons for the selection of the Micro USB. One is due to board real estate. The mini-USB consumes much more real estate and in a board of this size, real estate is precious. The second is for power options. Since the design offers full power options from the USB jack, it makes sense to utilize a connector that is already a standard for powering other small devices. Micro USB is now the standard in that realm, so that was the wise choice.

So, this is a prop board that will fit in a bread board, and all we need to add is power?
Yes, that is correct! The width makes it appear as if it blocks some access to a breadboard, but it's height allows room for jumpers easily.

I think I would want three to start with, when can we order?

We are working out logistics of the startup costs to kick off production and updates will be given as frequently as possible.

0.050" is not easy to work with, what about 0.1" headers in double row?
The 50 mil headers were selected based upon real estate and the ability to provide as much versatility as possible. Growing the board wider would restrict it from mating with some BS2 boards.There are 0.1" headers available that will plug into every other pin allowing you to gain I/O easily. Plus, we would be offering an expansion board to mate with the module for even easier connectivity.

If I may suggest, make a kickstarter.

That is an option, but we are looking at other avenues that fit the business model. This will be managed by a business already in place (kickstarter works well for startups) and we are focused in addressing on initial material costs. We are looking into pre-order type solutions that will provide that and enable quick delivery for early buy-ins.

What USB drivers, if any, need to be installed for this to be programmed?
Standard FTDI drivers as all Parallax's boards, etc. The only difference is the Propeller Tool needs to have the reset signal set to "DTR & RTS" under "Preferences:Operations". The FT230X uses RTS for reset since it does not offer DTR. This change does not affect functionality of the Propeller Tool for other boards with DTR.

Do you have a better pinout chart?

See pinouts on the Gallery page using the top menu bar. I created a pinout chart mapped to the 50 mil headers, odd pins of the 50 mil headers to get 0.1" pitch, even pins of the 50 mil headers to get 0.1" pitch, and the bottomside 24 pin DIP configuration. Also, I listed pin descriptions.