Kind of building on the idea of the crackly Skywalker saber, I think it could be interesting if during Kylo and Rey’s duel on the Death Star, that Rey’s saber was almost becoming “overloaded” from the constant saber-clashing, and starts shorting out by the end of the duel. For example, in the shot where Rey sort of shakes her hand, you could have the saber fluttering in and out. Then finally, when Kylo keeps hammering away at Rey while she is on the ground, we could see the saber give out while Kylo is raising his to deliver the final blow. This would give a reason for why Rey grabs Kylo’s saber and stabs him with it, rather than just using her own.
I think it would add an interesting aspect to the duel that we haven’t really seen before, where our characters are dealing with a malfunctioning weapon. It also gives Rey a practical reason for why she inevitably builds her own.