I wondered how my 2 year old would deal with potty training once we had the new baby. With this in mind, I've kept her in the blueberry trainers for the last few months even though she rarely had accidents. I figured the added protection when we had a baby and she might regress would be a good idea. She'd be spending a few days with her grandparents (and had never been away from us for more than an hour or two previously) so i thought that might cause some chaos as well.
However, she's done great! She had no accidents with grandparents or with all the new baby visitors when we got home. After a couple of weeks, she started having accidents at night (4 out of 5 nights in a row) but I think that was more about exhaustion than regression of some kind. After she started catching up on sleep more, the accidents stopped. She finally had one small accident yesterday (after more than 5 weeks of daytime accident free) where she suddenly announced she'd made a mess and ran to the bathroom. It was only a few drips and almost all contained in her trainers so not a big deal. This is the longest accident free stretch she's had, actually.
I wonder if we're not seeing any regression because her brother is going to the potty too. Perhaps that's a benefit of ECing that I hadn't considered before.