My understanding is that BA must interline with this carrier, this would suggest that they dont necessarily have to be in OneWorld, but also would suggest that easyJet would unlikely candidate. Yes EZY are low cost and many would say unlikely to be interested in LHR, but based on the EZY strategy of offering low fares to convenient airports, could we see them appear?
Interesting question.
I don't see why VS or U2 would want to get in on this market, as despite various bleatings about competition and slots, both airlines would have to make substantial changes to their business model to serve these two (remember just two) routes.
I would imagine BE would see it as a good way of making money for someone else by feeding lond haul routes, and they have history of staying out of LCY due to charges, not so sure about LHR.
Would EI take on the routes?
Maybe, but just exactly what does this agreement say and how can it place any kind of obligation on any airline to provide competition? If the market warrants it, an airline will deliver it.