Wing chun could be pretty interesting, as it, like Aikido, is pretty big into the center-line issue. Depending on the school, though, the footwork might be atrocius. Like many Chinese martial arts, it seems, proper footwork seems relegated to more advanced levels. But I'm sure your Aikido training will work that out pretty quickly.
You should also look into baji or xingyi. I have been impressed with both of those before and I think they would fit in nicely with your aikido training.
Totally go for Kendo. I practice it now when I find the time. It's a total blast. I think you'll actually find a lot of kendo very similar to aikido: incredible attention to distancing, timing, etc., and powerful body movement. And, hell, it's really, really fun.