Hi Guys, just sharing in case anyone else has this problem. It was a bitch to diagnose.
Had an issue with my 2016 i30 1.8 petrol, 150000k. At about 80 km/h it had a shudder or wobble. Only when accelerating. Stops as soon as your of the gas or get up higher in speed. Thought it might be the long cv axil but have changed it and still a shudder. Have had new tyres, wheel alignment and balance. Shudder was there before and after the change of tyres. No shudder in the steering wheel.
Turns out it was the right hydraulic engine mount.
Hope that helps someone.