Things have to go really bad from here, as I see it, for the office to underperform alternatives in the next few years, from a cash flow perspective. 

If this isn't an attractive alternative to your business partner then you might consider changing the ownership structure or operating agreement as one of your options.

Is Guesty or Lodgify a good alternative? 

These self employed 2nd mtg's are typically based on alternative method of caluclation like profit and loss statements if you're self employed or the last 12 months of bank statement deposits using a formula to derive an income from these deposits (like 50% of all annual rolling 12 calendar month deposits X 50% /12 months = monthly income).

Those that own real estate will want to be active, those who are limited experience and time look at it as an alternative investment and want an expert to manage it just like some hire a financial advisor for their stock portfolio.

Because your alternative is zero income.

I'm not sure how fast you want to scale, but I see that as a feasible alternative if you don't want to go through the process of either BRRRing or the fix and flip. 

I also recommend you discuss this with your tax advisor.There are many other alternative asset classes to invest SDIRA funds into. 

Therefore, I have a hard time committing to a house hack which contributes greatly to my problem of raising capital for a conventional mortgage with a 20%+ down payment instead of alternatives such as an FHA. 

And what's an alternative way similar to Jerry's program?