One of my favourite challenge playthroughs was only allowing myself to use pokemon that were classified as untiered on Smogon. It forces you to use a lot of weaker pokemon which require more creative tactics to succeed in some of the fights. Other than that, a lot of people on this forum use monotype teams to make new playthroughs more interesting. So, for example, only allowing yourself to use dark type pokemon. There's also things like nuzlockes, but they're extremely difficult and frustrating to do in Rejuvenation and Reborn because of how the games are structured, so I wouldn't recommend them.
Also I'd just like to add to this. Don't be afraid to take another break from the game until you're in the mood to try playing again. Reborn and Rejuvenation are extremely long, slow paced, and text heavy games. Like you said, it's very easy to get burnt out by playing them. I go through periods where I can't even get past the first gym without getting bored. But then I take a few months break, come back to play them again, and have a great time.