I think he would make a pretty good final boss if they upped his power a bunch. Maybe an extra final boss in some afterstory, where Wizeman completely looses any control and Jackle kinda just blows stuff up until NiGHTS pwns him or something. Considering that he doesn't appear to have a body, he could be everywhere, somewhere, over there, some crazy paradox location (for example, between you) or nowhere. And what a boss that would be.
i would prefer that if sega made a new sonic game, nights, reala and jackle were all playable
also it would be cool if jackle joined the neutral side
i mean, he gets tired of serving wizeman, and somehow runs away, fights nights, fights random boss, you know what i mean right? XD