I’m not aware of any distinction that “a college student buying/living near campus is not considered their primary residence”....talk to a couple of local lenders, I don’t see any issue. 

@Kim Rose Geographically speaking Grand Marais too Duluth and all things in between is no less than 4 distinctly different investing markets, each a fair bit different from the other. 

The San Antonio SFR market is also very difficult to analyze because there is no distinctive path of progress.

Sorry for the confusion on that - it is a critical distinction.  

This might be where a really good tax advisor would come in...If you could sell this property (or created a "deemed sale") to an entity that you control , but is regarded and distinct from you for federal income tax purposes, that might be optimal, if it doesn't cause problems with any loan or mortgage attached to the property.

There seems to be an important distinction of a Trust not being a "who," and that affects personal property and liability claims.

If you have a SDIRA and other funds to invest, you have two distinct piggy banks and they cannot be mixed.

Taylor Knight from Coldwell Banker Distinctive Properties

By filing a petition for bankruptcy, a person creates a bankruptcy estate.The bankruptcy estate is a distinct taxable entity—separate, that is, from the debtor’s estate that may retain any property exempted from the bankruptcy proceedings.Under the federal Bankruptcy Code, the debtor has no claim to this new creature of law, the bankruptcy estate.

So if the two units are roughly identical the you're good to go.You want to think of your replacement duplex as two distinct properties.