No, I think the length of the PS5(when laid on it side) is because of the 12 channel custom SSD controller setup and the resultant performance and how you keep that cool to maintain the performance by keeping them away from each other. I think the thickness/height of the ps5 is to house a double sided heatsink - making the overclock efficient - so at worst I would expect AMD cards to occupy twice the width of now ( 1 extra PC expansion slots bay behind as well as the 1 in front) but remain the same length form factor.
On the topic of Xsx and PS5 power, now I think about it, from Cerny's post-Road to PS5 interview with DF, he made the point about a new form of optimising for power in the PS5, as a real gain, so with the power supply comparison as it is, and the shift to constant power and variable boost clocks on PS5, it will be interesting to know, what that constant power draw is on PS5, and if it is more than peak power usage from the XsX when playing Gears 5 or Minecraft RT - which should be high occupancy and high power draw.
In the event the PS5's power draw is higher by a significant amount, then the "most powerful console" claim by xbox is false (and already over) IMHO, as computational capability of the PS5's APU will only get better as the generation goes on with power optimisation - going by what Cerny said, each and every power optimization will lead to higher frequency for the same workload - because the optimisation will have reduced the unoptimized workload occupancy - or resulted in capacity for new work to occupy the freed resource by optimisation, which leads to a higher computation per watt, in either situation.