Fewer and smaller S-boxes. It may be possible to reduce the number of S-boxes from four to one. Additionally, it may be possible to overlap entries in a single S-box: entry 0 would consist of bytes 0 through 3, entry 1 would consist of bytes 1 through 4, etc. The former simplification would reduce the memory requirements for the four S-boxes from 4096 bytes to 1024 bytes, the latter would reduce the requirements for a single S-box from 1024 bytes to 259 bytes. Additional steps may be required to eliminate the symmetries that these simplifications would introduce. Additionally, four different 10- or 12-bit indexes into a single large S-box could be used instead of the current series of S-boxes.
Just theoretically, how would using same s-box instead of 4 different affect the security of Blowfish (considering no other change is made)?
By "eliminate the symmetries", he probably means rotations? Is this really required, since round keys already break the symmetries?