All pretty rough ideas as I haven’t looked at all the CBMs in the game, but here’s what I brainstormed.
A CQC Synapse Booster CBM to increase Dodge, Block, and Melee upon activation could be a good high-end option for ‘melee’ CBMs without needing it to be a direct weapon within the body.
Something like a Sub-Aural Noise Field Generator to induce Nausea and/or lower Melee and/or Dodge in nearby beings that use hearing, perhaps?
Retractable Tentacle Array CBM (to fit in the Torso) could do double duty as Combat and Utility, acting as spare hands for the purposes of crafting/repairing/etc (in case your hands are full) as well as acting as an additional ‘weapon’ like the mutated Tails, Claws, Teeth, etc.
maybe a Phalangeal Pillar CBM installed in the hands to turn Bash damage from Unarmed to become fully Piercing damage, turning your hands into spikes with your fingers melded together (can’t hold things while active?)
Kinetic Absorption Precepts CBM which can turn damage taken during combat (aka: non environmental/hazard damage) into small amounts of power?
Mental Plasticity Enabler CBM that slows/stops Focus loss or even slowly gains you focus while active?
Dragon’s Breath CBM that lets you breathe fire through a sister CBM which provides an internal fluid tank, a-la flamethrower, but has a low-moderate chance to misfire (causing you to become Nauseous as you vomit up napalm/gelled gasoline/what have you) and has a lengthy reload time (as well as making your Mouth hot)?
Neuro-Electric Overflow CBM drawing additional power from the body (represented as damage ticks and/or heightened Stamina drain) creating an Incandescent Husk-like lightning bubble around the user?
Pineal Resonation CBM that greatly boosts morale and lowers Fatigue loss, but drains high power, makes you constantly visible to Nether creatures, and has a low chance of Teleglow or other negative effects while active? (I’ll admit, this one is more a ‘From Beyond’ reference than anything)
Gastric Intake CBM which allows you to implant a battery that can be charged by consuming Concentrated Acid, but which cannot be charged by other means and can malfunction to require uninstallation and mending?
A full-on Skeletal Re-integration CBM which replaces or coats the bones with metal lacing/plating, providing more health (or giving a chance for ‘break’ damage to not break a limb, like the metal is resisting being broken) but requiring full uninstallation and repair if any bones are successfully broken?
Or maybe something mundane, like a built-in kitchen system or very mini minifridge? I’d love an extra place to store some cold, fresh juice or meat.