Not just integrating servo-motors and all that fun stuff, but additional servo-motors and fun stuff. You can have barely above zero capability to carry anything beyond your own body weight (let alone a full suit of battle armour) and still be mobile.
That's just completely not true, both in 5th and 4th editions. In 5th edition, Mil-spec armor is still considered restrictive, the enhancements are enough to make the armor more protective while just as impeding as the security armor.
In 4th edition, the bonus of the milspec armor was that it allowed the wearer to have less Body before being considered encumbered (it changed the calculation from Body x 2 to Body x 3). This meant that a wearer still had to have at least a Body of 4 in order to wear the very lightest of Milspec armors.
The section you quoted was the part about adding the Mobility upgrade, so yes, the base armor has some servo-motors. These things aid
movement, it doesn't make the armor an autonomous unit. For example, on the very lightest armor (the Oyoroi armor with 11/11), upgraded with the maximum Mobility Upgrade R3; a character with Body 1 would still be encumbered at -1 to Agility and Reaction by this armor. Body x 3, compared to the 11 armor, is 8 points over-encumbrance, which results in a -4 penalty (1 per 2 points), compensated 3 points by the mobility upgrade down to -1. So Even the lightest armor with the best upgrades is not wearable, as you say, by someone "barely above zero capability to carry anything beyond [their] own body weight"
That's why it would be an upgrade, not a current feature.
If you want to get really fancy with fourth edition;
For wannabe street sams, superficial cybernetics are available that look like real cyberarms and legs at one tenth the price.
To hide your meat body, you can get modified cybernetic casings that make you appear augmented. Superficial cyberware can have some functionality like cyber spurs and blades, but they have to fit over the existing limb (items such as cyberguns or raptor cyberlegs cannot be included).custom strength, custom agility, tough and non-invasive external limb augmentation. It exists.
Pretty sure that the custom strength and custom agility aren't things that would be considered "non-invasive" or superficial. To get augmentations to Strength or Agility normally requires replacing musculature. And also note, that even if it did all that, none
of it enhances Reaction
which is what this thread is trying to argue.