The most liquid of the private investments are investing in equity or credit hedge funds, real estate funds, and private company funds. There will usually be 6 month – 3 year lockup periods. The least liquid of the private investments are when you invest directly into private companies yourself. You might not be able to get your money out for 5-10 years, depending on the success of the company and upcoming liquidity events.
But when so many turn down leasing one and one-half acre for one Wind Turbine for each 80 acres, that lease certainly does not materially affect the rest of the Farm or Ranch grazing pasture and the lease pays much more than the farm crow or grazing pasture lease, just because some lawyer said the lease was too long: 30 years plus 30 year option = 60 years, and the wind turbine company has selling production/electricity contracts for the next 150 years – which is needed to obtain financing!

In mid-2017, I sold my San Francisco rental property for 30X annual gross rent and reinvested $500,000 of the proceeds in real estate crowdfunding. I’m leveraging technology to invest in lower valuation properties with higher net rental yields in the heartland of America. With the new tax policy starting in 2018 capping state income and property tax deductions to $10,000 and limiting interest deduction on mortgages of only $750,000 from $1,000,000, expensive coastal city real estate markets should soften at the expense of non-coastal city real estate.

It’s obvious that stocks outperform real estate in terms of capital gains, but I would like to see S&P compare to Real Estate in SF, Manhattan, LA. Our house in NC was $80,000 20 years ago. It’s only $150,000 now. Same house in Santa Monica went from $200,000 to $1.8 million. People who happen to bought real estate in major metropolitan would have a natural positive association with real estate investment.
Residual income is the best model for money generation. Once you master and build up one avenue, you can devote your time and money into another avenue. Eventually you start reaping the benefits of multiple residual income avenues. Enabling you to have complete financial and time freedom. I recommend to all people to build these types of asset models as they can greatly improve their life.
One of the things I'm surprised your article doesn't mention is the tax advantages of this type of investment. The depreciation and rehab costs (purchasing distressed properties) can be huge deductions to ones income taxes, which none of the others have. Then, along with the appreciation of real estate, this passive income investment outperforms the notion of maxing out my 401k as well.
If you're looking to get started in real estate, look at a crowd funding solution like RealtyMogul. It works similar to LendingClub - you commit as little as $5,000 towards a property. When the property is fully funded, you become an owner, and will receive your share of the earnings and appreciation in the property.  Check out RealtyMogul to learn more.