Saw Rogue One. Overall, It succeeded most in how it emphasizing the toll of getting the Death Star plans, leading right into Episode IV. Solely watching Episode IV, you're thinking, "okay, whatever, rebels have Death Star plans." After watching Rogue One, I have a deeper appreciation for plot.
I compare Rogue One to Walken's "butt" speech about the watch in Pulp Fiction. Take that out and you have less of an appreciation and understanding for why Butch (Willis) goes back into danger to retrieve his watch. You'd kind of just accept that Butch does. The following action would still be enjoyable without Walken, but just provides that extra oomph.
In any case, for a person that has never seen any Star Wars that's about to watch them, how would you order the viewing? Still Episode IV-VI first? Would you then go VII after or back to I? I feel like you'd want to show Rogue One somewhere in the middle, leaving Episode I-III last.
I think Rogue One, then IV - VII would be an interesting way to watch them.
I think that's all there are, right?
However, doing so, I think that viewer would be more interested in the plot and the rebellion, whereas we grew up focused on the Force and Jedi. That viewer might get turned off in V, wanting to see more battles than Skywalkwr in a swamp training.
Hell, I might not show that person Ep I at all and just show II and III last.