I think if they are going to the extent of making their own generic RPG system then it's a pretty safe bet to assume any new L5R RPG product will use some variant of this system. Also I guess it's no surprise the system uses custom dice considering that's how their current big RPG system (Star Wars) operates. They've put out other RPG products in the past that don't use custom dice though so it's not a sure thing. The End OF The World series uses D6s. The Warhammer 40K RPG used percentile dice. Though they do seem to as a company favor custom dice systems. It does help further obscure the math, which is a good thing in my opinion. On the down side it forces you to use their dice instead of all the cool dice you've already collected.
I guess it doesn't matter to me either way. I wasn't in love with the roll and keep system. I do prefer systems where the GM doesn't roll at all (like in the Cypher System). Unfortunately FFG's Star Wars game is definitely not that. I also prefer systems where the players feel like they have tools to mitigate luck. I don't recall how FFG's Star Wars system was in that regard.