Hot Water Dead Legs

When a hot tap is turned on unless the fixture was recently used there is a time lag for hot water to flow. This occurs when the water in the dead leg cools over time, the cool water must first discharge before hot water will reach the outlet. 
The question often asked is "what time lag is acceptable" and "what is good design practice". Should it be 5 seconds, 10 seconds or is longer acceptable?  

As shown in the table below, a 15mm pipe with varying dead leg lengths significantly impacts time lag.

Note: 15mm has been used as an example, the dead leg lengths nominated do not comply with AS3500 in all instances.

What can be concluded from this information? Are dead leg lengths restricted by new low flow tapware? Are hot water systems becoming more complex with longer circulating loops to reduce time lag?

It seems reasonable to assume dead legs over 10m to a single fixture will push the envelope for end user satisfaction.

It should also be pointed out fixture flow rates have almost halved in recent times but the way we design hot water systems and the regulations controlling design parameters has not been amended.
Is it time for a change?