He can explore if he qualifies for a partial exclusion under section 121 (Pub 523 here)...a deployment isn't specifically listed, but job related changes are, and it does say other non listed events may qualify.

The only remaining options to consider are if you could qualify for a partial 121 exclusion based on selling for a job transfer etc, or looking into investing into a qualified opportunity zone project.

You cannot take section 121 exclusion if it is not a primary. 

If it was posted by a realtor I am assuming they have an exclusive contract to show so you may as well keep using yours and let them do their thing.  

Regardless of what they tell you as far as "exclusive" or only sold 2-3 times its all a bunch or "BS". 

MM has an exclusive engagement agreement where 1% of total sale price is asked whenever this agreement is signed regardless if you use their recommendations for financing or you choose to shop the lending with another commercial lender?

If you prefer to keep it...just sell it and buy a similar house in the same area so you don't loose the capital gain exclusion on the sale of a primary residence (and you get the higher basis in the new property to depreciate).

and is there any way to get exclusions to that, or would it be better off to do a 1031 exchange on such a property? 

You can only take the 121 Exclusion once every 2 years.  

Kyriko, I cannot stress how happy I am that I am finally in the process of dumping my own snooty condo across the road from Pittsburgh's most exclusive mall.