Yes, and no.
Thanks for the detailed reply
Really....
Why?
It is not limited by hardware. (depends how want think)
Highest true sensitivity in DS1000Z is 5mV/div.
After then 2mV and 1mV/div is only digitally vertically "zoomed".
What you get more if you zoom more.
ADC have 8 bit. 256 theoretical levels. (if look more deeply not really even this, ENOB, analog front end noise etc)
2mV/div (simplification) 128 levels.
1mV/div (simplification) 64 levels
do you want zoom more.
If you look this scope quite noisy front end (analog front end + ADC) noise, do you get something more if you zoom more.
It is totally other case IF there is good low noise amplifier before ADC so that with 5mV pp signal it use ADC full scale. (around 10 div vertically on the display)
Finally: Lowest true sensitivity in DS1000Z is 5mV/div.
This is truth least in my DS1074Z.