Hi,
Time really flies, 10(!) years for Signal path soon. Keep it going, it is an excellent technical channel.
I would be interested in working principle of PLL. PLLs were mentioned many times during teardowns and reviews, so it is a good topic to review in greater detail.
Other, shorter topic could be calibration procedures of VNAs - how to check for proper calibration, how to estimate calibration coefficients for calibration standards, how to estimate port extensions, etc.
Also, Signal Path lab has grown over the years and currently looks nicely organized (all instruments are accessible, mains cables are hidden). You could make a short review on mains wiring and shelving solution in a lab, i.e. how you manage to not run out of mains sockets