It will be costly, but cost well spent, as higher production rates unlock economy of scales advantages that make the plane even more competitive. If they can bring it to around 25 frames per months on 2 lines, they should be well set.
Sure, but it's no small ask for the rest of the supply chain to double their output by a factor of two, or actually 2.5 since the original target BBD set was 10/month.
Then you need to feel you can reliably sell 300/year for long enough to pay off all the facilities needed to double the scale of the production line.
And then we have all the strategy issues around the Airbus/BBD/IQ partnership to consider.
Above it was written the current plan is to get to 14/month in 2024.
It'll be interesting to see if an improved plan gets put into place or not.
They don't need to increase production yet. Look at a simplistic ramp of increasing each site by 1 a/c per month each year. Start with 5 per month by the end of this year for Mirabel and 0 for Mobile, proceeding to 6 for Mirabel and 1 for Mobile by the end of 2020 and so on. You end up with over 700 total frrames produced by the end of 2024. Or a capacity of ~600 between the start of 2020 and the end of 2024.
Their order book also has lots of wishy-washy orders (Odyssey, Republic, Red Wings, Braathens, Ilyushin, Gulf Air). About 100 or so orders that are doubtful. So that makes the real backlog as of today about ~430. That leaves plenty of room for DL, B6 and AC to up their orders and possibly even 1-2 more larger customers jumping in before Airbus even entertains ramping further, let alone steepening the ramp or adding a new production site. That said, they are getting close. If some of those ambiguous orders actually turn real, they'll quickly end up in a place where they need to ramp higher and/or faster.
I don't think the limiting factor here is the supply chain. Their suppliers will deliver if asked. Happily. They now have more business than they could have ever hoped for with BBD. The issue here is still demand. Airbus needs more orders and customers to justify further investment. They'll also need to sort out the program ownership issues with Investment Quebec and Bombardier before they really commit to substantial investment. They aren't really rough problems to have though.
On topic, the rough math above says that Air France could get all its 60 frames by the end of 2024 if they want.