If you’re trying to prepare for a couple of years in advance, it might be worth spending a day playing with each language just to see which one feels best to you. Both languages should be able to do anything you want but some things will probably be more difficult in one or the other. I’ve never used swift, but I know rust can have a rather steep learning curve. That may be deterrent enough for some people, but that’s up to you to decide if that struggle is worth it.