I do not think that they qualify, because their function as delay lines did not depend in any way on the fact that they happened to use a liquid medium.
Delay lines with sounds or elastic waves can be made using any propagation medium, solid, liquid or gaseous. The only desirable property is to have a low velocity for the waves. Also it may be useful for the propagation medium to be piezoelectric or magnetostrictive, because that simplifies the transducers from and to electric signals.
While the mercury delay lines were important for a small number of the first electronic computers, some other early computers have used delay lines made with magnetostrictive metallic wires.
The delay lines can also be used as analog memories, not only as digital memories. As analog memories, they have remained in use for many decades after they have been abandoned in computers, e.g. in the color TV sets or in radars. All later delay lines used solid glasses or crystals, not liquids.
