I don't really understand the SG stuff, but all of the other ideas sound recycled. The weather system has been already somewhat implemented in FF13, what are you trying to accomplish with it this time, are you trying to add on to it, or what? Your day/night idea has already been in various game series, like Enix's Dragon Quest or Atlus's Shin Megami Tensei (it was BIG for this series) games.

Summon/Weapon levelups? Already been done (ff8/ff13).

I think they could be pretty fun to implement, but it all depends on execution. What do you have in mind?