  Transition-edge sensor (TES) bolometers are broadly used for
background-limited astrophysical measurements from the far-infrared to
mm-waves. Many planned future instruments require increasingly large detector
arrays, but their scalability is limited by their cryogenic readout
electronics. Microwave SQUID multiplexing offers a highly capable scaling
solution through the use of inherently broadband circuitry, enabling readout of
hundreds to thousands of channels per microwave line. As with any multiplexing
technique, the channelization mechanism gives rise to electrical crosstalk
which must be understood and controlled so as to not degrade the instrument
sensitivity. Here, we explore implications relevant for TES bolometer array
applications, focusing in particular on upcoming mm-wave observatories such as
the Simons Observatory and AliCPT. We model the relative contributions of the
various underlying crosstalk mechanisms, evaluate the difference between
fixed-tone and tone-tracking readout systems, and discuss ways in which
crosstalk nonlinearity will complicate on-sky measurements.
