I really doubt that L5R will start out or even rise to the heights of most of the other LCG's.
Star Wars, Lord of the Rings, Game of Thrones, these are international franchises with far reaching popularity and while card games are by comparison to the rest of the franchise a very tiny, insignificant chapter, they have name recognition. Legend of the Five Rings is a virtual no-body even in the gaming world, I'm 40 years old and have been gaming for 30 years, much of it at conventions, stores and events aside from my core group and I can count on one hand the amount of people I have ever met that have played or ever even heard of the card game. You can go to a gaming convention like Gencon and never run across a single L5R card the entire weekend.
None of the LCG are particularly big by any measure, in particular when you compare it to something like Magic The Gathering but L5R.. I mean there are people in this very post who discovered it through FFG's announcement.
Personally though I'm rooting for it. This is without question one of my favorite settings ever put to paper, I'm more excited for this then anything that has been announced and released in the last 10 years.