I'm curious if there is anybody (best of all in Europe) who would like to produce a soldered multi I/O board in a small series consisting of
2x PCF8574 (1x8 digital in, 1x8 digital out plus transistor motor output stage)
2x PCF8591 (2x4 analog in)
For power supply connected to a Lego battery box (6x 1,5V) we could have 1 i2c board not bigger than 10cm x 6cm with
8x touch sensor in
8x motor on/off
8x analog in
Plugs/connectors could be, e.g., in NXT style or - very cheap - in RCX style (similar to Mindsensors Rx muxers).
the PCF8574 part may look like this (courtesy of Bernhard http://www.mindstormsforum.de/viewtopic.php?f=73&t=5306&start=30#p61317
The most expensive parts would be industrial etching boards,
and the price for everything altogether including workload could be far <80 EUR for selling.
I guess there will be lots of interested people to purchase something like that.