I punted on currency conversion, but I will implement it at some point – the app is currently front-end only but the economical way to do currency conversion would be to write a scheduled task to pull the data once a day (e.g.
from the ECB's website) and store it in a JSON file that gets served to the client. Expect to have to write CAD instead of $ for Canadian dollars – I'm US-centric.
The Canadian Brim credit card is interesting to me, and I will add it. I'm going to rely on FTers to suggest non-US credit cards to include – I'll consider them based on (a) a notable mileage earning that does not require purchasing the ticket with the credit card or (b) notable first-party lounge access. I'm not sure if the audience for this tool will care about the annual Sky Club passes that come with the Japanese credit cards, but that's now competitive with the US Amex Platinum and Delta Reserve so please let me know if there's interest.
I'll add a default airline and fare class – when the tool was solely a Delta tool it was safe to assume DL Y since RDMs are based on the ticket price, but now that the tool is getting more complicated I think it's worth the additional interface complexity.
Just to clarify on the default airline and class....create a field where the user can set those defaults (like the "other" site does).
I think we are on the same page, but after thinking about it, didn't want you to assume I meant to set the default for FB to AF/A for everyone!