unfortunately, no consensus could be reached on how to address the concern that namespacing railway would be a suboptimal solution. There were a few other secondary tags proposed on the Tagging-ML, but as there were no direct responses from the OpenRailwayMap-ML it's currently impossible to progress this proposal any further.
I have set the proposal https://wiki.openstreetmap.org/wiki/Proposed_features/Deprecate_railway%3... to Canceled. If there are any future developments, everybody may feel free to reopen the proposal.
I'm sorry that consensus couldn't be reached.