Hydrogen would be a viable alternate use for the pipelines in the long term. There are some promising projects going on in Alberta for producing hydrogen in less carbon intensive ways.
Making a pipe leak tight to hydrogen versus leak tight to oil is not even playing in the same ballpark. Hydrogen leaks through practically everything, oil is viscous.
Plus hydrogen burns much more easily and the flame is transparent.
Atomic radius of helium is smaller than hydrogen 31 vs 53 pm. Hydrogen gas is also typically in the form H2, which is much larger. At the same time ofc oil pipelines will still be too leaky.
It seems it's hard to transport pressurized hydrogen in pipelines as hydrogen embrittles steel. Gas utilities are trying to implement this to lower the carbon footprint of their gas (when hydrogen comes from renewable sources).
I hypothesize that a hydrogen leak is less destructive than an oil leak, but that's still a problem.