EZY would never order the C-series, it goes against the simple LCC principle of having one type of aircraft
To a large extent the rule book has gone out the window in relation to LCC's, or their precise definition. Take JetBlue for example, it has a second type commensurate with the markets that it wants to access that would not suit A320 family. Another ingredient would be the use of secondary airports, but that is clearly now not the case. Ryanair even now go to FRA, which they said they never would. Norwegian now have long haul, a step change in terms of operating model, and as a result a operating a wide body.
EasyJet is more of a value carrier than a pure LCC and with its European peers operating at a lower cost it will need to have a point of difference. A type with lower costs to operate at a reasonable frequency may be a USP.
If the business case stacks up, such C Series coming to the market with a lower cost to get scale of orders or visibility with particular carriers, the likes of easyJet or any airline should consider looking at it. Building such business cases naturally is about more than the purchase price, it will need to look at type rating costs of pilots, maintenance, and a host of other nuances and costs. Again if it stacks up....
EI-BUD