To bring the turtles and Splinter to life in a new movie my preferred method would be go back to the animatronic suits and use cgi to animate the faces and correct for when the suits look visibly rubbery and for stunts etc. I know I'm not alone within TMNT fandom in thinking some variation of that is the best way to go. However I know that it's a long shot and realistically if/when a new TMNT movie series starts up again the studio will want to to go full motion capture cgi again because that's just the 'in' thing.
Regardless of whether it is a soft or hard reboot they are not going to use any variant of the pre-existing designs so like the first Platinum Dunes release the main bulk (of what I presume will be a lower budget) will be eaten up by creating entirely new 3D models. Practically this means we will be looking at another release were the human actors carry the majority of the movie.
While many fans including myself railed against the 2014 movie for waiting 17+ minutes to properly introduce the turtles but in hindsight I wonder is this such a bad thing?
In most versions it makes sense to lead with the turtles but a lot of modern comic book movies don't have the hero establish their identities right away. They set up the world and it's rules first and with TMNT they were taking an interesting idea of the April O'Neil investigating a new crime fighting force. Trying to make the turtles seem intimidating and mysterious is a good idea in my book and even helps sell the idea that these are ninjas.
Friends who I went to see the 2014 movie with who weren't TMNT fans thought the first part of the movie were trying to do something different and interesting with the turtles before the tone abruptly changed and we got Michelangelo farting in his brothers faces
. I've seen some online reviews from people who likewise are not fans say similar things.
This failed in two ways though.
1. The build up to the turtles was still inconsistent. It's hard to sell a New York City which is being routinely terrorized by a paramilitary criminal gang when April is bouncing on little trampolines and no one seems all that concerned about them. I'm not saying the turtles NYC needs to be portrayed as crime ridden like Gotham City but the 1990 movie established the underlying threat of the Foot in their world, heck even the 1987 animated series did this in it's opening episode.
2. Megan Fox. This may sound harsh since she to be the target for a lot criticism that should be reserved for the film maker she is most associated with but we really need a better actress for April. True, we don't need an oscar winner to play the lead in a Teenage Mutant Ninja Turtles movie but if an actor is going to carry the movie and we're going to get a extended period of watching little but them then they need to be engaging.
So this is just some food for though in the likely event that in the next movie we may have to have plucky investigative journalist April O'Neil going all X-Files on the turtles in the first 20 minutes.
Of course just because it has to be led be human actors doesn't mean it has to be April. In fact this may be an opportunity to do the full Hamato Yoshi & Tang Shen murder story which we've never seen on the big screen before. Maybe it helps us better understand Splinter's motives but also Shredder's too. After all if Thanos can have understandable motives to wipe out 50% of life in the universe then we could finally get a version of the Shredder to does things for more than just being evil for evil's sake.