The only part I disagree with, and it’s just my opinion, is that I believe 50/50 entails less overall risk than 100% TIPS, in a large taxable account, meant to provide for a 30+ year retirement.
If you are talking about Dr. Bernstein's idea you first have to have enough. By that he most likely means that all your nest egg isn't tied up in the TIPS ladder. He says the rest you can invest anyway you want even 100% equities.
So, let's say a person has a nest egg of 1.5 million and need 40k per year to supplement other income. 40k x 20 + 800k. So, Dr. Bernstein suggests putting the 800k in a TIPS ladder or other "safe" products and invest the rest as you wish. So you could have 47/53 allocation if you put all the excess in equities. If you only had 800k I don't think anyone would suggest you put it all in a TIPS ladder.
My personal opinion is that you want to end up with at least 30% in equities and have some fixed income not dedicated to the liability matching assets.
50/50 is a reasonable allocation. Just remember in retirement most people have little human capital, are withdrawing instead of contributing and will be withdrawing even when the 50% equities takes say a 50% drop. Which is likely to happen a time or two in a 30 year retirement. Are you still going to rebalance all the way down? It is a lot different situation than when you were working and contributing and getting a company match and maybe even a bonus.
Lets use the example above using a 50/50 allocation a 50% equity drop and the end of year 1 would put the portfolio at 375k equities and 710k fixed income or 1,085,000. approx 35/65. Now it is time to consider rebalancing and taking 40k out for next year. That is pretty much a worst case scenario.
It will likely feel different in retirement. No need to panic. But being down almost 1/3 of your nest egg can cause some sleeplessness. If you had 19 years worth of drawdown or 760k left in TIPS or other "safe" products you might get a bit more restful sleep.
The key question is if you really have enough why not secure your retirement funding first and then determine the overall allocation instead of "guessing" that the top down allocation will do fine. For most that have enough it will likely mean changing the nature of a good portion of their fixed income. Not a big deal if fixed income was targeted for stability.