>It might be possible considering that Drosera regia's closest relative is Aldrovanda.
This doesn't appear to be true. With no disrespect to Rivadavia et al, in the rbcL MP tree, it's important to notice the low bootstrap support for the regia/aldrovanda clade ,the arcturi/rest of drosera clade, and the split between these two clades. The rbcL data simply don't strongly support the hypothesis that Aldrovanda and regia are sisters in a single clade, and the authors note that Aldrovanda and Dionaea show up as sisters in their larger dataset, with much higher bootstrap support. The same authors report different chromosome numbers for D. regia and everything else in the family, so this is probably a good reason to doubt that regia can be viably crossed with anything in the family. ('X and Y are different genera' is a less compelling argument, just ask the Laeliocattleya breeders.)