Hi Bob,
Well, that "real estate" component in the chart on p. 34 has to be filled with something, and I think one can infer from his discussion on pp. 75-76 that he's fine with filling it all with TREA. (Similarly, I don't think Bogleheads are too far off in concluding from his discussion on the remainder of p. 76 that they can fill it with Vanguard's REIT index fund . . . ) It's certainly not possible for the average REIT investor to mix in TREA, and I'm at least not aware of his ever suggesting that the average TREA investor would be better off splitting their 20% RE allocation between TREA and REITs . . . Nor am I saying I think he'd be against diluting TREA with REIT's, I just haven't seen him say that, have you?.
All best,
Pete