So I was one of the unlucky owners of a 13 Ecoboost with a myriad of problems including the timing chain rattle. A lot of warranties will not cover unless you are getting a sensor light. However, videos of the rattle are very helpful. I would record your cold starts and try to get a handful of videos with the rattle and take it from there and show your dealer.
Also, if you get your warranty to cover it, make sure they replace the phasers. I have read numerous cases where the chain only was replaced and the rattle returned quickly. However, to your question - on the early generation Ecoboosts, the timing chains seem to stretch regardless. Ford has shown repeatedly that they consider this a "wear item" and aren't concerned about it. Therefore, I don't think another chain/phaser fix 80,000-100,000 down the road is unlikely. However, you can help avoid it by running more frequent oil change interval (5k instead of 10k regardless of what the computer says), using Motorcraft filters, and running a good full synthetic. Sludge is a major contributor to the rattle and long changer intervals with cheap oil is a great way to get sludge.
That all being said, I ended up running Mobil 1 high mileage extended performance and Lucas Oil stabilizer and it actually stopped the chain rattle after it had done it for 40,000 miles. It is also important to use a Motorcraft filter. They have a better check valve than most of the aftermarket filters and prevent the oil bleed-off overnight that causes the dry start and the rattle. I have also read about guys adding Seafoam to their oil before their change to break up the sludge and had the rattle stop after the next oil change.
I'd like to add before I get a bunch of hate mail, yes I realize that the increased viscosity of the high mileage oil and the additive were simply coating my chain and only stopping the rattle but not actually "fixing" anything. However, search the internet far and wide, please find me one case of where the rattling chain actually did fail. My attitude is that I would fix it the day my engine light came on, but before that happened, I was in a wreck that totaled it and I took my insurance check and bought a 5.0 FX4 and haven't regretted it once.