I understand the anxiety of not knowing how it's going to work, but it could be that the RS allows you to go in the LL and meet up with the rest of your party as they are about to board so that you can then ride together. The way it works now, the only thing preventing those with RS from getting in the LL immediately after the rest of their party enters standby is that they have a child too short to enter the queue so they have to wait until the rest of their party is back to ride. With these new changes, you might be able to time it so the rest of your party in standby gets to the boarding area around the same time as you do through LL, perhaps with you or them waiting to the side for a couple mins for the others to arrive.
Yes, you would still be separated for those lines, but realistically, it's not that huge of a part of your day. If the above scenario I described is possible, you'd still get to ride everything with your entire party (if not you'd still get to ride with one other person), and you still be permitted one other person to wait with you presumably. Plus, there are oftentimes shorter lines that many people with disabilities would be able to wait in with their entire party without needing to use rider swap. Plus, the time spent with the entire party walking around the parks, dining, having snacks, watching shows, meeting characters, animal trails at AK, parades, fireworks, looking around shops. There's still loads of time that can be spent with the whole family. Being separated while queueing is a relatively small amount of time in the grand scheme of things.
From the way it sounds, it's not going to be specifically a "potty pass" but rather a leave the line pass available for anyone who needs to leave the line for any reason. It could be someone with IBD having a bathroom emergency, it could be a non-disabled person having a bathroom emergency. Or it could be someone who needs to test their glucose/administer insulin and isn't comfortable doing it in line. Or someone having a low that needs treated and they don't have any snacks/drinks. Or someone feeling nauseous suddenly and needing take a break. So I don't think anyone is going to just assume that someone has IBD or Chrons. I really doubt the CMs are going to ask why you need to leave, nor are they going to require you to register for this in advance. Disabilities or not, there are numerous reasons why someone might need to leave a line, and this has always been accommodated in the past, with no need to explain your reason. I've left lines numerous times and for the most part never gave a reason (though to be fair it has always been for legitimate bathroom, dizziness, anxiety, or hypoglycemia reasons). I just notify a CM and they take me out back ways so I don't have to backtrack through the line.
While there's no way to know for sure yet, I imagine returning to the line will also work similarly to the way it has before. As long as you tell a CM you are leaving the line, they put a LL pass on your acct and you enter through there after you take care of your issue. I've never had to try to fight my way back through the standby line.
I've heard stories of people who have tried getting back through to their party in the standby line and how difficult that is. I don't know if that's because they didn't tell a CM they were leaving and therefore didn't get a LL pass or if some CMs just told them to re-enter standby to find their party and didn't offer a pass. To me, this leave the line pass sounds like a continuation of the accommodations that has already been in place, just advertised so more people are aware it exists and therefore don't try to push through the lines to get out and back in and to clarify any confusion amongst CMs that may not have always handled the matter consistently.
If all of this works similarly to the way it has, then there would be no need for anyone, CMs included, to know why you are leaving the line and since you're returning through LL, no one would know you even left, let alone the reason why.