At this point, I rather they give the series a rest.
IF they must make another game in the same vein, then focusing on a new character/characters in the same setting would do wonders to prevent the same sort of kikery we saw after the Future trilogy.
Where DO you go from there?
A second reimagining or post Into the Nexus?
Secret Agent Clank was a ... "good" game at the time. Clank as a secret agent, a spy game of sorts. I actually remember that Clank had a role as Secret Agent Clank in Up Your Arsenal.
They made it into a full blown game.
The premise was that Clank is investigating a stolen artifact called the Eye of Infinity. Only he found out that Ratchet ... DID it. As Clank, you investigate who stole it and clear Ratchet's name.
You play as Clank, Ratchet and Qwark in different gameplay loops. Stealth, arena and brawler. Ratchet's gameplay is more arena based, you fight waves of enemies in the prison. Clank is more "stealth" with a bit of action. Qwark is more brawl based.
I put "stealth" in quotations because it's barebones. It's basically quick time events and Elite Beat Agents rhythm based. It's dull to say the least.
Ratchet's gameplay is a slower version of the arena challenges from prior games. It's passable but doesn't have the thrill as previous entries. Weapons are weak, gameplay is slower.
Qwark's involvement is that he's writing a biography and he makes stuff up as he goes. Think Up Your Arsenal's vid comics but 3D and the premise changes.
In short, it's a passable entry but lacking in many areas for the Ratchet & Clank saga.