His business markets to the majority of Americans with very little financial savvy for saving, eliminating personal unsecured debt, and building wealth.

Since the loans are unsecured you need more money to close that loan and 40% OR 50% down requires that you pay more down.The SD-IRA account allows more flexibility when investing but is very much opposed to you getting any of the profit until you reach retirement age. 

They plan on giving me an unsecured LOC with 80k limit.4.

You might want to also look into a personal unsecured loan or line of credit if you're credit is good) it'll be paid off sooner than a higher costing property and you can cash flow better, sooner.

What we will not allow is unsecured debt to be the down payment or closing costs because, historically when that was allowed, some huge percentage of the time that "unsecured" debt was recorded as a 2nd mortgage on the subject property the day after closing, thus entirely defeating the purpose of "skin in the game."

:Real estate related loans often tend to be secured but if you have obtained an unsecured loan, absent of any condition or restriction by the lender on the use of loan proceeds, you obviously can use the funds for any legitimate purpose -- including real estate investing. 

Has anyone approached a bank / financial institution to propose opening an UNSECURED line of credit solely for use to buy, rehab and either hold or flip?

I think an unsecured loan of this size would be difficult to come by and, if you found one, the terms would not be as favorable as a mortgage.

I have a decent size unsecured commercial line with a different lender with no deposit account.

This would all cut into my return and suck up unleveraged cash for an unknown time period.