Nomura said FFVII Remake's materia system is basically the same as the original's, and that since the battle system has been revamped there will be new materia to match it and some materia will disappear. This is to a question Famitsu added to the online interview.
Personally I'm thinking you will have (and need) less materia slots than in the original, if only because the late-game weapons would look ridiculous with the visible slots on them.