It is very unlikely that the largest companies today will keep up with the market to remain the largest into the future. These Mega Cap names tend to under-perform. This chart is a great visual of what history can teach us about how quickly these names can drift out of favor. 
Also, here is a look at the number of Top 10 names that have historically drifted from the largest 10 over the next decade. The average in the U.S. has been around 6-7 on average.
#RobArnott referenced this fact in his recent Barron’s interview, and it’s one of the ways he point out that index funds tend to Buy High and Sell Low.
barrons.com/articles/rob-a…
barrons.com/articles/rob-a…
This is also a point @jposhaughnessy made in his original version of What Works on Wall Street.
We have also discussed it in more granular research like our REIT paper. “More than 60% of the REIT index is in the Largest 20% of names…and those names have underperformed the REIT market by 2.1% annualized”
osam.com/pdfs/research/…
osam.com/pdfs/research/…
Most investors can do better than market cap weighted indexes.
