To save time and effort, a person can group two or more of their passive activities into one larger activity, provided they form an "appropriate economic unit." When a taxpayer does this, instead of having to provide material participation in multiple activities, they only have to provide it for the activity as a whole. In addition, if a person includes multiple activities into one group and has to dispose of one of those activities, they’ve only done away with part of a larger activity as opposed to all of a smaller one. 
However, I think for those who are willing to do what it takes, the sky is the absolute limit. As an example, I’m trying to take a page out of FinancialSamauri’s book and create an online personal finance and investing blog. It is an enormous undertaking, and as a new blogger, there is a seemingly endless amount of work to be done. That said, I hope that one day I can not only generate some passive income from the hours of work I have put and will put into the project, but I hope to be able to help OTHERS reach their financial goals.
Consider refinancing your mortgage if you haven’t done so in a while before interest rates go up further. Or consider leveraging cheap money responsibly to acquire hard assets. LendingTree Mortgage has one of the largest lending networks online, and they will contact you immediately with their offers. You want lenders competing for your business, and get hard quotes so you can pit them against each other. 

Secondly – and this is just quibbling – I’d change that risk score. The risk of private equity is incredibly high and should be considerably riskier than bonds! You are providing a typically very large amount of capital to one business that you agree to have no control over, and the success or failure of that business over a locked, predefined term determines your return. And in the few deals I’ve negotiated for clients, my experience has been that there are often management fees, performance fees, etc. that may cut into your potential gains, anyway. You’re putting a lot of eggs in one basket, and promising an omelet or two to the management no matter what. You really need to be confident that you found the next Uber before you take this giant risk!
Mike, I don’t consider the income from FS to be passive, as I’m spending time commenting to you right now. But since 75% of my traffic comes from search, the most traffic I would probably lose is 25% for probably a year. And then my search word rankings would probably slowly fade given frequency of posting new content is one of the search algo variables.
For those of you who don’t want to come up with a $220,000 downpayment and a $900,000 mortgage to buy the median home in SF or NYC, who don’t want to deal with tenants or remodeling, and who wants to not do any work after the investment is made, check out Fundrise. They are my favorite real estate crowdsourcing company founded in 2012 and based in Washington DC. They are pioneers in the eREIT product offering and they’re raising an Opportunity Fund to take advantage of new tax favorable laws.
It is very important to understand that contacting a “professional” to learn how to do this only results in them trying to sell me crap properties (whether high end or low end). I’ve tried contacting realtors out of state, and they attempt to sell me crap or someone else’s problem. No one has a vested interest in actually helping someone or teaching them about how to get an out of state rental. very frustrating. I could go out tomorrow and buy a rental in my city, but that is the last place I want to own one. Anyone? Are there an real people on here?
Creating passive income is the key to retiring, especially retiring early. If you want to retire early with the stock market you will have to save a huge amount of money, because that money has to last so long and retirement calculators depend on you using your investment to fund your life. With passive income you will have income coming in as long as you own the investment, without every eating away at the principle invested. Creating passive income may take more work than investing in the stock market, but I think it is well worth the extra effort!