The bosses in the Regular clockworks tend to have been done by the vast majority of players.
And seeing the typing of the current bosses, there would be space for two Crimson Order bosses in Tier3 (one typed Constructs, one typed Gremlin)... and one Fiend boss (looking like Hajime Satomi? (Joking!)) in Tier1.
This would give us 3 Tier3 bosses, 2 Tier2 bosses and 2 Tier1 bosses - let's face it, the Arcade needs new things, and bosses costing ridiculous amounts of energy (or real money) to enter aren't exactly popular.
After this the typing would be Beast (Gloaming Wildwoods), Fiend (Corporate Restructuring), Slime (Royal Jelly Palace), Puzzle (Ironclaw Munitions Factory), Undead (Firestorm Citadel), Constructs (Construct Assembly Plant) and Gremlin (Darkclaw Experiment Site).
With concept art!
I'm pretty sure you'll find at least a couple Tinkinzar boss threads if you use the search bar.
The Roarmulus Twins already satisfy the Construct family, but I'm certainly not against the idea of having a second Construct boss.