It kind of triples your likelihood for a deal to fail.The truth is that, for most of us, a successful flip or BRRRR without the tailwind of appreciation during the renovation period is really hard.

For example, if the seller initially agreed to pay 2.5% agent commision and the buyer now wants some repair credit during attorney review period.

Over a longer hold period, your return on equity will eventually drop.

Their  rate changes periodically and as interest rates rise so does the imputed interest rate. 

Seasoning is just an industry term for waiting period to use the improved value to pull out cash. 

seasoning in lending just means a waiting period.

Since "perpetual" also crosses the 30 year period that the IRS likes for these kind of things. 

The issue I have here is that once those funds are gone in a few years, we will then have to cover the entire cost myself (~3k) for an indefinite period of time.The other option is convert it to a rental. 

Quote from @Carlos Ptriawan:  They believe that they will increase the properties NOI by 45% over 5 yr hold, mostly through rent increases after doing 5K interior upgrades in all 252 units, thus adding 19 million to value of property. how is it possible increasing rent 50% in 5 years period in place where comps and rent is decreasing, this local market is extremely saturated.For me if I have to buy in Austin I would find complex that could give DSCR 1.3 at least with 80% occupancy.if they increase rent 50% then we should do intelligence on their closest neighborhood's rent. 

It is part of your due diligence period.