So far every keyblade wielder in KH (except Xion) has, no matter how many keychains he or she gains, one keyblade that is his/her personal and iconic weapon.
For Sora this one is the Kingdom Key, I doubt that this will change.
Riku has his Way to the Dawn,
Ven has Wayward Wind (which is curiously up to now the sole keyblade designed for his backhand-style, his other keyblades are all normal ones just held backwards).
Roxas has his Oathkeeper and Oblivion, Terra his Earthshaker and Aqua her Rainfall.
The only one's to get an upgrade of sorts are the last two, Aqua and Terra...and in my personal view I think it should remain that way. Just like with the armor and the gliders I think it won't be good if Sora gains everything the other original characters have...leave some things also unique to them.