actionman
Emperor Mongoose
I could definitely see subdermal armour being an elective option for troops expecting to be deployed into heavy fighting. Particularly those who routinely operate Battle Dress, where every point matters for surviving stuff like automatic gauss weapons loaded with APDS and you're already spending a lot of money per soldier. Or high-end mercenaries and special forces, where you're really trying to concentrate as much force and skill in as small a space as possible.
Stuff like the Soldier's Organ Package shows us that there is room in the setting for spending a lot of money on individual soldiers sometimes (Even if it's not a regular occurance), and subdermal armour is a drop in the bucket compared to that, plus it doesn't come with horrible early aging and sanity altering downsides like the package.
Some thoughts:
There are two different trains of thought happening in this discussion. There's the logical-intuitive train of thought, like me thinking about long term medical effects of subdermal armor and the problems of heat dispersion in brain cyberwear, and then there's the other train of thought about the MgT game mechanics, which create the de facto reality in game. These two trains of thought aren't compatible, and the game mechanics create what is true in game, plus whatever house rules the ref implements. The game mechanics create the in-game reality, and the logical-intuitive thinking must be developed from that reality. So, according to the reality created by the game mechanics, the logic might be completely different. The question should really be, "The rules mandate this is true, so what must the logic be that reaches this already mandated conclusion?"
So in the in-game reality created by the rules, it may very well be that every soldier getting subdermal armor and cyberwear is the most logical course of action for Traveller militaries.
In general, when the game mechanics create a reality that is grossly illogical or fails to have a plausible cause and effect for things in its de facto reality, it creates uncomfortable cognitive dissonance, that feeling of things not making sense. People respond to this by making house rules, or ignoring things, or by refusing to discuss issues. Each occurrence of this weakens a game as a whole, and if there are enough of these problems, people have to house rule so much that they're essentially playing a different game. People can make things work, but they shouldn't have to.

