For those without other income, unwrapped assets can obvs be used to generate income.
However, for those with other sources of income, & who may look to liquidate prior to ISA & SIPP:

The 60/40 pf is forecast to return 6% ish annualised next 10yrs.
£100k compounds to £179k.
Less so after tax, if the capital is liquidated.
Assuming the cap gains allowance reduces to £1500pa from £3000pa currently,
For a basic rate tax payer,
I reckon that's a 5.2% annual rate of return after tax.
For £200k, 5.1% after tax.
Obvs worse for higher rater (ref. fiscal drag...)

The current compound rate of the 10yr low coupon Gilt is 4.6%, effectively tax free.

Is it worth bothering with unwrapped risk assets,
esp if it'll be tax efficient to liquidate & spend those before ISA & SIPP?

I have a fairly chunky GIA and about half is in low coupon gilts and the other in risk assets that I deem to have lower downside risk than a passive fund (hold things like PSH, Berkshire, Fundsmith). These have no or very low dividend yields also. I expect them to slowly compound long term and will deal with any CGT issues as and when; hopefully in future the CGT thresholds and rates will be more favourable.

I actually have a cash ISA as I find it more beneficial to use it for cash than Berkshire/FS etc. Low coupon gilts come with a sacrifice of yields and tax on savings interest is 20% and a certainty.

I estimate my overall tax bill on a 7 figure portfolio will be a few hundred at most.

This is a really important calculation to do. And if the estimates turn out to be along the right lines, there'd be a good argument.

This is sort of the equation CGT, PNL and Ruffer are doing – estimating there's more (at least risk-adjusted) value in treasuries.

I would say, if you're largely tax-sheltered, and able to get closer to 6%, then assuming inflation's 3-4%, you're comparing a real return as low as 0.6% to a real return of 2-3%. Roughly three times the return. I would say that's worth it – but you could certainly justify going to something like 40:60. In fact, even in the worst case for stocks, I'd still not go below 25% stocks – I don't think it's wise to sit out the market.

I'd also note that return estimate was about the same in 2014, from memory. Not to say it's a bad estimate – but there's still a very wide margin of error, and returns can come in funny sequences (you could quadruple your money before things fell off, and that's why you always want to be in the market).

The other risk of going all-in on gilts would obviously be inflation. That could decimate a portfolio really designed for deflation. I think the takeaway is you can justify being more balanced and diversified than 60:40, but if you've been 60:40 for a while, there's probably still more risk in doing something than doing nothing.

Rather than the 10yr nominal, consider index linked bonds instead in the GIA. Most of the gain is tax free at maturity and real yields are good at the moment.