For Glory is their version of "Competitive" Smash and in competitive Smash there are no items, not even the Smashball.
The Smashball would defeat the whole purpose of that, although they're already kinda defeating it by only allowing Omega stages. I think the only way I'd accept the Smashball in For Glory is if it only stayed in the Free-for-All Mode where there's four players instead of just two. On 1V1 we only have two stocks and a Smashball (depending on the character) can make things really lopsided quickly especially considering there's only Omega Stages. In Free-for-All though it's based on time instead of stocks.
Otherwise, I really can't see a Smashball existing in For Glory and would rather not have it.