The English speaking community sure has a smaller impact on them than the French speaking one but it's still an impact (+ French speaking subscribers are quitting too).
Plus covering the costs of servers alone should not be enough, even if Dofus 2 isn't their main goal anymore they should at least aim to go for break-even on it. Otherwise their profit margins will drop since afaik Dofus is still their main franchise.
Also like I said, it's an interesting idea combining Mobile and PC-gaming but I don't know if that's the route they should go. I may not be from 'the new generation' (what letter did they give it again?) but shouldn't Ankama aim to get people hooked/addicted? I mean mobile games quite often have a short life(/hype)span because of their 'mobility'. (e.g. Pokemon Go)
Imo you'd want people to get so hooked that they don't mind playing for 12+h a day and I don't think the mobile aspect will help for this. Nor will naming it Dofus 3.0 since it'll help to get people interested in it at first (since they play(ed) the game or heard of it) but they'll also directly start comparing it to Dofus 1.0 and Dofus 2.0.
Dofus 3.0 could quite possibly become a success but not the way it's marketed right now.