Hmmm, I didn't think about that. 

Generally, if a Residential Rental Property were to change to a Nonresidential Real Property, you would keep the original placed in service date but just switch to the longer Recovery Period.  See Regulation §1.168(i)-4(d)(4).  I would THINK the same would apply for a 1031 Exchange, but I'm not 100% certain.

https://www.law.cornell.edu/cfr/text/26/1.168(i)-4#d