I have a customer asking me to make a 3 tiered cake in buttercream, but she wants all kinds of fondant rope decorations... ropes in like scrolls & heart shapes glued to the sides of the cake. I'm worried the ropes will be too heavy & fall (or roll) off of the buttercream icing. Is this possible?

When you mean ropes, do you mean quill work, like the hearts on this?  

I wouldn't mind having this on the ABC I make, but I can see where something like a cream cheese frosting would not work.  Do you have time to experiment a bit with the buttercream you use?

No it's not the flat bands, its more like actual ropes. Kinda like the hearts on this cake... 

If she wants that much of ti it would be safer to put it on fondant. If it's thin like the ones in the picture you attached those would be okay on buttercream, but put the cake in the fridge to chill it after it's decorated to keep it all in one place.