E.g. members entitled to 50/50 untaxed distribution after accounting for 100% return of capital to capital contributors, all outstanding costs of sale, accrued taxes (?

.§ 5.075.Purchaser's Right to Pledge Interest in Property on Contracts Entered Into Before September 1, 2001(a) On an executory contract entered into before September 1, 2001, a purchaser may pledge the interest in the property, which accrues pursuant to Section 5.066, only to obtain a loan for improving the safety of the property or any improvements on the property.

I accrued my first sum of seed capital while working in the service industry as a young man.

I have never had this problem, but is there any tax law that allows for accrued revenue for year 2015 vs having to claim it in 2016?

It could be zero, or it could be significantly higher than the amount shown on the mortgage if the credit line was increased or they haven't made payments, resulting in accrued interest and penalties.  

So, you can use the cash value and all interest accrued over time tax-free (because your taking it out as a loan).  

 $300k becoming $600k is a little extreme, but of course years of accrued interest, insurances, taxes, etc. do add up.

I've been accruing some rentals over the last couple of years in the area, but I'm currently getting my feet wet with my first flip!

Interest can stop accruing as a function of law.  

You could put the student loan into deferment and stop making payments (and if they're subsidized loans they wouldn't even accrue interest), while still collecting the cash flow from the SFH.