Quite a few things would need to be changed .
I've compiled a list
(BTW, I'm basing this on a possible TV series)
1. Sleeker, more human designs: Characters would have to look the part of a biomechanical being, with a more proportionally human figure.
2. Change setting: This may sound a bit drastic, but it really isn't. There would just need to be more of a sci fi element to the story. Not as much open wilderness, and more integration with Metru-Nui style technology.
3. Villians: They'd have to be MUCH creepier. Rahkshi: go all out. Spines, poison, tongues, jawless maws, everything. Same with Visorak and Barraki.
4. Powers: Less of a focus on elemental powers. Possibly even replace them with less close-to-omnipotent powers, even possibly just their mask powers ('cus I mean, judging by the theories in this forum, most Toa are super-powered).
5. Phasers: To make up for fewer powers, and to add some thrill of a fire-fight, add phasers you can set to stun.
6. More mature jokes: Bionicle has some pretty lame jokes. You'd need to make 'em mature to appeal to a more adult audience.
7. Romance: This is pretty much a requirement for a young adult or adult audience. No romance = no interest.
I'm probably missing quite a bit, but Bionicle would have to change quite a bit to fit into a TV series that would appeal to adults (however, I would LOVE to watch it).
Edited by Paleo, Jan 23 2013 - 10:08 PM.