Ya know you don't have to have a fancy shmancy zanpaktou ability. You could just have a melee type which is what ichigo's is. Melee type zanpaktou don't have any unique abilities and instead focus on increasing the user's battle capabilities such as Ikkaku's Hozukimaru, Renji's Zabimaru, Shuhei's Kazeshini, and Zaraki's new Nozarashi.

which speaking of I don't think increases such as an 10% strength or speed increase should have time limits and cooldowns. Just because they have a little more strength, speed, endurance, etc doesn't give them an overwhelming advantage. As long as it's a reasonable increase to a max 2 areas then it doesn't need limitations like that.