You simply can't repurpose a natural gas or oil pipeline into hydrogen without re-sleeving it and doing a number of other retrofits. It's not easy, and it will be a while before that technology scales up to a point where it's cost-effective.
Having said that, if hydrogen is used adjacent to where it's produced, the cost of storage and transportation can be quite low. For example, for hydrogen that would be generated near a city like Vancouver and then input into the natural gas grid, either at 20% through an existing pipeline or at 100% through a dedicated hydrogen pipeline, those economics could work at some point in the future.