Like the custom endocrine systems of combat sleeves in Richard Morgan’s Altered Carbon edit: I think I was thinking of Iain M Banks’ “Culture” series actually, but both are worth a read! Need to be strong or fast? Just give yourself a little squirt of adrenaline! Time for slow heart rate and low energy use? Slow-release a skoche of acetylcholine.

You make a good point about subscriptions. The repo when you stop paying would be pretty grim.