So this was done only with Sodium, imagine what Cesium, Rubidium or Francium might do?
Another just "what if" scenario, taking a chunk of sodium and firing a waterjet cutter at it.
The other metals will have different parameters of surface tension, voltage (though not much more than the voltage of sodium), reaction rate and so on, so they may simply react spontaneously (probably with the same explosive mechanism), more or less.
As for the waterjet, the reaction rate will be significantly enhanced; it might simply blow away faster than it's able to explode (en masse) though! The fragments will of course react quite rapidly once they go off on their own.
Aside from what was already mentioned about trying to measure the current generated, I'd like to see this experiment take place inside a sealed pressure vessel, not so small that it would explode, but one where you could measure the pressure spike inside it.
You could also use a pressure sensor to detect the leading edge (and rise time) of the shock wave.
Besides hydrogen, steam (and maybe some sodium metal vapor, too) should be part of the blast.
And yes, another thing to keep in mind: sodium metal has a relatively low boiling point, around orange heat.
Tim