I've spoken with 5 reputable nationwide HML's s far, and all have restrictions around proof of funds for the down payment. 

Correct, the loan to value restriction protects their interest.

But also look out for potential rental restrictions, I'm in Los Angeles, and a lot of condo HOAs have limits on rentals so the overall % of rented units doesn't go over a certain threshold.

My dilemma is made worse by the fact that there is nearly no inventory in this market with favorable short-term rental specs (no HOA, no land lease, no rental restrictions from the city, etc.), and this property fits them all. 

Rules can change and put restrictions on rentals.Prices may go up, but I wouldn't depend on it happening-it is the icing on the cake.You can also look at nearby areas where you might be able to get a good single family house for the same amount of money.

The license will restrict you in a dramatic way.

I think most of the time when people think of budgets, they think restriction...Think Planning and Control instead. 

Agreed on the City of Everett being very restrictive when it comes to conversions.

Different cities have different rental regulations (rental license, inspections, etc), and also if there's an HOA, they have their own restrictions but nothing currently statewide.  

Pennsylvania COVID-19 restrictions limited real estate activity, with the lowest level of new pending sales in six years, while Philadelphia Metro reached a record median sales price and ten-year low for days on market.Cheers,Yuriy