Upper limb rehabilitation exoskeletons face fundamental challenges achieving coordinated multi-joint assistance within portable configurations. Current cable-driven systems demonstrate effective single-joint support but lack coordinated shoulder-elbow capabilities due to anchor-point sensing constraints that limit workspace during simultaneous movements. To address these limitations, this paper presents a novel coordinated 3-Degree of Freedom (DOF) shoulder-elbow exosuit (3.3 kg) employing motor-proximal sensing architecture. Strategic load cell repositioning from anchor points to actuation unit locations eliminates spatial constraints, while geometric compensation algorithms maintain measurement accuracy, enabling coordinated assistance (shoulder flexion/extension, abduction/adduction, elbow flexion/extension) with preserved 0–$90^\circ$ kinematic workspace. Systematic development integrating product design specifications, multi-criteria decision-making, and biomechanical component dimensioning provided traceable design synthesis. Preliminary proof-of-concept tests with healthy participants (n = 5) provide an initial assessment of the system performance, demonstrating adequate sensing accuracy within the primary Activities of Daily Living (ADL) workspace, measurable muscle activation reduction, and preserved natural kinematics with minimal range-of-motion (ROM) constraint. An extensive experimental validation is out of the scope of this work. Results establish technical feasibility for coordinated cable-driven assistance, identifying requirements for future clinical translation.