Well, first off, the 2003 show should already be on there and I know Rise is coming. I would also also assume the PD movies, the 2012 show and possibly those shorts will be on there. I assume the Fred Wolf cartoon, the OVA, the 90's movies, the 2007 movie and Next Mutation won't be due to copyright issues.
As for original content? As in what I would like or what's more probable?
In terms of what I would like... I do have some ideas of what might work:
- A series of more accurate animated movie adaptations of the major Mirage Studios arcs.
- A series adapting IDW up until issue 100 (Just change it so that Jennika and Krang really die, Hob's bomb fail and a few other key changes to tie up the loose plot threads).
- An movie, possibly live-action, based on Last Ronin.
- Standalone shows featuring characters like Casey and the Fugitoid as main characters, not so much spin-offs as attempts to make these characters work divorced from the TMNT.
But as for what's probable... Nickelodeon is on life support, it'll probably get shut down around 2025 or so, maybe it'll last beyond 2030 but I seriously doubt it. The kiddy section of Paramount+ (which might get labelled as Nickelodeon) will probably replace the channel, meaning the new TMNT content on the service won't be too disimilar from the 2012 show or Rise.