The third future Rider is Rento Makina A.K.A. Kamen Rider Kikai. He will appear in episode 23. He comes from the year 2121, where he fights to protect the last surviving humans against the 'Humanoids' - machines that look exactly like people (so even if they stop the rise of Oma Zi-O, doesn't this suggest that the human race is FUBAR anyway?). The suit of his transformed form is based upon a Guardian robot from Build (although I think the helmet comes from something else? Possible a highly modified Grease helmet?).
And if that double denim outfit and robot-based suit and backstory weren't all big enough hints that this is something of a tribute/reference to Kikaider, he is being played by Jingi Irie, who played Jiro/Kikaider in the Kikaider REBOOT film a few years back, and was most recently seen as the villainous Zamigo in LuPat.
Looking further ahead, the three Riders will combine their powers (in a way that reminds me of Den-O's Climax Form) to become Zi-O Trinity. That's Geiz's face on the right shoulder and Woz's on the left. The toy comes out in March so expect to see this quite soon.
He is going to have to wait until May, but Woz will also get another upgrade. It will, of course, come in the form of another power taken from a future Rider. In this case, Kamen Rider Ginga (seen in the small inset picture at the lower center). This will allow him to become Woz Ginga.
Finally, this gaudy monstrosity is Grand Zi-O, his final form. Thankfully, we won't be subjected to this until June.