GI Joe, thank you for your service. Guaranteed payments are usually used like salary in a Partnership, and will reduce the Qualified Business Income (QBI) from the Partnership, but they are not counted as Wages for the QBI Wage/ Asset limitation rule. You are correct that guaranteed payments do not exist on a Schedule C, or a single member LLC filed on a Schedule C, however the net income from Schedule C is reduced by 3 Self-Employed items (½ SE tax, SE Health Insurance deduction, Pension deduction) to get QBI from a Schedule C.

For a 1065, there is no requirement that guaranteed payments be populated- it is based on the operating agreement or up to the operating partners. I suspect this year, the collective GPs will go down, and the 1065 Ordinary Income will increase, as a logical extension of tax strategy.  No idea if IRS will expand guidance about GPs in the future.

To see how QBI, Wages and GPs interact across entity types, you may want to play with the Entity Selection Calculator here:  https://proconnect.intuit.com/tax-reform/entity-selection-calculator/

Hope this helps.