I think that there is another possibility as well. The European division of its space program into commercial/exploration sides has a interesting advantage in that, because the launchers are commercially successful, they are always available to the space agency when it needs them. Because of this, if Ariane were to develop a heavier launch Ariane 6, they would keep it (in contrast to Saturn V and the Soviet heavy lift, which were not commercial programs). Now, ESA/ Ariane were talking about an Ariane 6 in the past, but at that time Ariane V was not a commercial success. Now it is, they just put in an order for 35 more. If Ariane decides that it would be more efficient to put more than 2 satellites in orbit at a time, we could well see a larger rocket. The designers at Ariane need something to do now anyway. Couple this with the fact that ESA would buy some heavy lift capacity if available, and perhaps they are kind of on the fence. Now, if NASA is hinting that they would also use the new rocket, Ariane would go for it. Maybe that is why NASA admin is in Guyana now. They want an insurance policy in case something happens to the Aires (lesson learned from STS) and are letting this play into Ariane's calculations.