The channel length is independent of the Gear and PAM level. It is 15m for coax and 10m for STP and STQ cables.
Yes. The specification for the connector is part of the complete end-to-end channel definition.
A-PHY provides information on link quality and multiple indicators on channel status that can be used by the application per user definition.
Cable loss is modeled in the A-PHY channel model, the values used in this model were based on available data for cables and connectors recommended by various OEMs.
MIPI A-PHY v1.0 defines coax or SDP (shielded differential pair) cables. There is nothing in the specification that prevents UDP (unshielded differential pair) implementation.
A-PHY v1.1 doubles the total downlink bandwidth from 16 to 32 Gbps by adding support for Star Quad (STQ) cables that provide dual differential pairs of conductors within a single shielded jacket. This enables two A-PHY ports over a single cable, saving cost, weight and complexity compared with using two separate coaxial or shielded twisted pair cables.