Regarding the A340-200/300, just study the wing planform, dihedral angle and 2 outboard engine locations....
Airbus used the basic A340 wing for the A330MRTT, but used the outboard engine locations and plumbing to supply the AAR pods. You can't do that on the A340; even if it was aerodynamically and structurally possible to fit pods outboard of the engines (which I doubt - it isn't a 707), considerable design work would be needed to supply the pods with adequate fuel flow rates. The process of clearing receivers against a 'new' tanker design is also a very time consuming and expensive activity, except for UOR 'heart of the envelope' clearance during TTW.
Of course Boeing knows all about the problems of buffet and flutter caused by poor pod / pylon design on the original KC-767, so if a major manufacturer experiences such difficulties and programme delay, it's unlikely that anyone else trying to fit pods on an A340-200/300 would find it straightforward - or cost effective. For example, the UK wasted £M through a sub-contractor trying and failing to fit AAR pods on the TriStar; it might eventually have worked, but by then there were more VC10s available anyway, so the programme was dropped.
Whereas pre-owned A330-200/300 would merely need the existing A330MRTT wing and pod modifications - even a boom if really necessary. Quite how much life is left in pre-owned A330 aircraft is a different question though.