They are keeping the original suit, I’m sure that whoever makes the armor can make it light enough that he doesn’t have any difficulty wearing it.
The TV series constructed a lighter version for Richard Eden to wear, so it's certainly possible. It could probably be made even lighter today.
My prediction is that Robo will be CGI. Perhaps mo-capped by Weller, voiced at the very least.
In the action scenes, sure, but for dialogue scenes and the like, it makes more sense to use a physical costume. CGI is good for creating images that can't be created for real, but for something that can be created for real, like the RoboCop costume, the real thing is always going to be better. If there's an issue with Weller's ability to wear the suit, then his motion-captured lower face could be matted onto the double who wears the suit onstage. VFX works best when you mix techniques and choose the best one for each particular goal, rather than trying to do every single thing with the same technique.
I don't think Weller would be needed for performance capture for Robo's overall movement. The reason for performance capture is to replicate an actor's distinctive performance style, but RoboCop's movement style wasn't really Weller's; it was created by his movement coach, choreographer Moni Yakim. It's a style of movement that was learned for the movies by Weller, Robert John Burke, and their stunt doubles, and for the series by Richard Eden and his stunt double Ken Quinn. (And not learned by Page Fletcher of the Prime Directives miniseries, which is why he flailed around ridiculously like a kid in an oversized Halloween costume.) So if anything, it would be better for the suit to be worn, and for any necessary performance capture to be done, by a dancer or stunt performer who could duplicate the official RoboCop body language invented by Yakim.