Many of the GNSS solution providers like UBLOX and Telit have families of devices with the same pin-outs and form factors supporting various features.  In the case of Telit the SL869, SL869-V3, SL869-ADR, and SL869-3DR.  UBLOX has the neo-5, -7, and -8 generations of families that are pin=compatible upgrades.  Personally, I am interested in Untethered Dead Reckoning (UDR) as implemented in the UBLOX Neo-8U and the Telit SL869-3DR; and RTK as implemented in the UBLOX neo-8T.  It would be cool for TinyCircuits to offer an upgradeable GNSS shield using one of these pin-compatible GNSS families...especially if you implemented the shield with a socket so it could be tailored by the customer for their application!