I'd like to start by saying that I have no quarrels with TTV's old project "Brickonicle." But it never really excited me. It never felt like the BIONICLE I grew up with. Here is what I would love to see with a BIONICLE reboot. I created these custom parts, and I plan on making all 12 BIONICLE masks as visor clip-ons for helmets ala Knights Kingdom. I will be working with friends on making to-scale system sets of Mata-Nui. The beach is where BIONICLE belongs, and the Toa behemoths woke up on that beach. And I wouldn't want my "Brickonicle" any other way. I currently only have basic figures completed, and I know for a fact I would not be able to submit this to LEGO ideas due to custom part issues.
The Matoran arms would be made of a soft plastic similar to that of the shoulder parts from the NEXO Knights robots (https://www.bricklink.com/v2/catalog/catalogitem.page?P=22392#T=C)
I do plan on 3D printing and casting all the new parts at some point in the future.
Hopefully, this interests the TTV community, and I can't wait to hear your feedback.
[I used Stud.io, Custom part creator, and Blender.]