So… while that’s true of most astronav systems to date (particularly the ones meant to be used during daytime, and especially with reference stars potentially near the horizon), I’m not sure that’s really a hard requirement.

If you restrict the domain to nighttime or exoatmospheric, a high-resolution wide-angle camera paired with an offline astrometry database has the makings of a strapdown astronav.

Widening the domain again, the natural motion of the vehicle is probably enough, when combined with inertial sensors to aid pixel-shift image stabilization, to achieve the same kind of processing gain as the older systems got with shutter-synchronous detection.