So, as mentioned in other threads, my wife and I are nomadic.

I have considered taking over his cash out refi because i heard it mentioned one time before but i cant find any info on how to do this. 

"Want" is a personal preference and I would defer it until the end of their lease unless they are asking for it in which case they have to relocate for the work.You are probably in a situation where you are waiting at least a 1/2 month of rent and maybe paying for them to stay in a hotel or short term living space for the work.

We just don't have that much of them, so I wouldn't hold your breath waiting for a unicorn, because when one does hit the market, there are 1,000's of others waiting for the same thing and many are cash buyers. 

When the son eventually sells the house, does he have to wait 2 years starting from May or November to get the 250k primary residence capital gains exclusion?

You're options are limited if you want to retain 100% of the equity have others have mentioned, but their might be some creative options if you're willing to split equity. 

Section 8 is a common form of rental assitance in our area, however wait times for tenants to get approved due to demand/limited funding can be significant.

Like mentioned, every market is different.

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The numbers showed that option 2 closes the performance gap as I approached my target retirement age (65+) and exceeded it in retirement.My calculation does not factor in equity appreciation - just compounding of present value.I like the fact that option 2 gives me income while waiting for retirement.