What would a clean-sheet set of wiring regulations look like today?

Putting technical topics to one side, I think a big improvement could come from simply re-writing the document from scratch with an improved structure which groups all of the requirements in a more coherent, logical way and removes the fragmented, rather disjointed structuring of the document. As these types of very long-lived documents get steadily amended over many decades, everything new tends to get tacked and bolted on to existing document as a series of extra paragraphs, extra subparagraphs or extra sub-sub-paragraphs, new sections. It all becomes rather incoherent over-time.

I would also look at the governance arrangements for how the Regs are modified, so that new requirements added to the Regs have clear risk assessments and financial assessments which are publicly available to demonstrate and justify why the new requirements were added, to bring some demonstrable rigor into the process.

Related to this, I'd also add a second companion document, which captures the 'why' details about each requirement. There's a failing common to most standards and regulations, that documents set out what is required, but the reasoning and justification to explain how those requirements have been arrived out is often not documented, or poorly documented but that's actually quite valuable information, particularly for those requirements which are quite obscure, where the 'why' is not readily apparent, or where the 'why' may become invalid over time so call into question if the requirements are still necessary generally.

I might also add a clearer process within the Regs governance, for people/parties to raise topics, issues or modifications to get things changed or improved, or to address contradictions or incompatibilities which emerge.

Putting technical topics to one side, I think a big improvement could come from simply re-writing the document from scratch with an improved structure which groups all of the requirements in a more coherent, logical way and removes the fragmented, rather disjointed structuring of the document. As these types of very long-lived documents get steadily amended over many decades, everything new tends to get tacked and bolted on to existing document as a series of extra paragraphs, extra subparagraphs or extra sub-sub-paragraphs, new sections. It all becomes rather incoherent over-time.

I would also look at the governance arrangements for how the Regs are modified, so that new requirements added to the Regs have clear risk assessments and financial assessments which are publicly available to demonstrate and justify why the new requirements were added, to bring some demonstrable rigor into the process.

Related to this, I'd also add a second companion document, which captures the 'why' details about each requirement. There's a failing common to most standards and regulations, that documents set out what is required, but the reasoning and justification to explain how those requirements have been arrived out is often not documented, or poorly documented but that's actually quite valuable information, particularly for those requirements which are quite obscure, where the 'why' is not readily apparent, or where the 'why' may become invalid over time so call into question if the requirements are still necessary generally.

I might also add a clearer process within the Regs governance, for people/parties to raise topics, issues or modifications to get things changed or improved, or to address contradictions or incompatibilities which emerge.