My basic thesis is that Trader Joe's makes it money not through offering odd items like wasabi covered almonds, but by deliberately undercutting the prices of grocers that have unionized work forces.   In states with right to work laws, such grocers would be far and few between, leaving very little room for Trader Joe's to undercut the prices of existing retailers.  If my thesis has any validity, Trader Joe's would show a strong preference for setting up shop in non right to work states, while avoiding right to work states.  I took a look at states that have right to work laws and compared to a list of states that have Trader Joe's.  This is what I found:

Trader Joe's operates in 26 US states.  22 states are right to work states.  Trader Joe's only operates in 6 of the right to work states.

Now, this obviously does not prove that Trader Joe's deliberately attempts to avoid right to work states right now or will continue to do so in the future.  They right now are saying they will open in Nebraska.   As they grow more established, they may consider it worth their time to move into less lucrative markets.