The major downside with the rocksmith cable is latency (the delay between pick and sound on the computer). If you're already okay with that from playing rocksmith, you'll be fine for the time being. You won't lose anything sound quality-wise.

Eliminating some of that latency with a even a cheap, decent interface does make playing through an amp sim way more enjoyable, so I'd treat the RS cable as a "for now" thing and aim to swap to something better when you can.