has anyone updated to stainless braided flex brake lines on the rear?

Britpart DA7561 is the only set i can find a reference to.

Goodridge dont do for LR/RRS 2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE

Why would you? Braided hoses might have a benefit on a sports car (and its debatable even then if it's a pure road car). They'll offer little, if any, benefit on a 2.5 tonne "truck". 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

What is the theoretical benefit of these types of hose ?

They're supposed to improve brake response and "pedal feel" by reducing the expansion of the inner pipe, as I understand it. The sort of thing lads used to (perhaps still do) put on their "hot" Fiestas to make them go (or rather, stop) better.

There might be an argument for the braided outer reducing the chances of damage to the brake hose itself, although I would have thought that any grit that got in there would act like sandpaper between the braiding and the hose. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

wasn't considering it for the benefit of performance...

more so for the benefit of corrosion resistance.
and the braiding is plastic coated so no question of particles or debris working through the braided steel.... if they are as good quality as i've had before from Goodridge (used on various BMW previously with track usage etc).

this is the 2nd RRS i've had and its amazing how much corrosion builds up in a few years over and around the rear axle.

that said, i would sooner replace OEM parts 2 times than put some rubbish on there.... so hence the question if anyone had done this change and any feedback 2007 TDV6 RRS HSE..now gone
2012 3.0 SDV6 RRS HSE

It is my understanding that Land Rover recommendation is that flexible brake hoses be changed every 6 years?

I like you had asked the question about a stainless steel kit on here before. Having used Goodrich hoses on a number of different cars and bikes I believe they not only offer exceptional value for money in terms of quality, but are also alot cheaper than the genuine hoses themselves and come with a fit and forget unlike the rubber equivalent.

Im not interested in the performance gains, just quality and value for money.

Sadly I couldn’t find anyone who made them  2003 BMW M5 - 5 Litres of V8 Optimax Slurping Goodness in Carbon Black

2013 SDV6 HSE Black Edition- Orkney Grey with Ebony & Ivory. LR Facelift RAI, Genuine G4 Expedition Rack, 4x Warn SBD-160 Spotlights, Warn 9.5XPS Winch, Mantec Underbody Protection and Sump Guard, Full Easy Lift Suspension Module, LR Light Guards, Light Force HTX230 Hybrid spotlights, 18” Compomotive PD1881 on 265/65/18 BF Goodrich KO2, ARB fridge, TuffTrek awning 😎

My Jaguar left the factory with them fitted (got brembo)

The advantage to RRS owners is you should not need to replace them again
and no rubber exposed.

If you use your RRS for offroading then they probably aren't for you