Someone who lives nearby might eventually give us an eyewitness report. Like the first year’s gravel loop this one is not covered by Google’s street view imaging. Last year however you could do a virtual ride of the loop on Google to get some feel for it. In the end I would say that if you have honed your gravel skills on the previous two year’s loops and supplement that with whatever gravel riding you can find between now and the end of July you should be well prepared to deal with this year’s loop.
I doubt they will go out of their way to pick a particularly challenging loop. The RAGBRAI planning team has stuck with the gravel loop for three years now and if that means they have a long term commitment to it then surely they want to see the gravel town rewarded with more riders than it had the last two years, although last year was not too shabby. Picking a particularly difficult loop at this stage of the game would not be a wise move.
In large part gravel riding is a mental hurdle. Convince yourself that you can do it and you can. Suitable equipment helps too yet many of the people you will see on the gravel loop will be riding bikes ill-suited to it so you don’t have to bring anything special to ride the loop if the notion that riding anything except a zero weight road bike on 23mm tires offends you!
Don’t worry about the loop, just ride it.