I also learned on a steel string, and still regularly play classical music (as well as popular music) on it; even though I now have a classical guitar.
I find I have issues handling the transition (either way, actually) for about 5 minutes and then it's like I never left one way or the other.
I would assuming if you were going from pure nylon string guitars to a dread-acoustic, you would be met with some challenges the first time; e.g the higher degrees of accuracy in fingering and hitting the strings, due to the smaller working area.
If you want a true challenge, at least from the right hand preservative, try a steel string 12 string. I just cannot get the knack of finger-picking it... Mine is stuck as a strumming beast for the near future!
Armed with Book, Forum, and Guitar, I will bare my teeth and face the world! Music is a way of thinking, an art. There is nothing more demanding, and nothing more rewarding.