Daniel Spilker made a nice spring loaded ICSP connector for programming AVR microcontrollers. We’ve seen similar solutions before; like the Tag-Connect.Most of these designs have the advantage that you don’t have to solder a header. However, when the locating pins are included in the footprint, the overall connector footprint remains the same.
In the T400 we use a regular surface mount 2×3 header footprint and connect to it using pogo pins similar to the Pogo Pin ICSP SPI Programmer Adapter on Tindie. I think if I were to deviate from the standard 2×3 0.1 inch pitch connector, I would put the pins inline to make board routing easier.
After searching the internet and browsing serveral print catalogs, I found the AVX 9188 Staggered SOLO Stacker in DigiKey’s print catalog. Its spring-loaded contacts provide a good connection for all pins. The idea for the ISPtouch was born.