Remember that banking and finance is full of regulations, and have moving speed of snail. Opposite of IT. When asked for something like this (open source or cross compatibility or anything nerdy) the first question is "who will be liable for losses and damages when something breaks?".

Liability is probably the biggest factor. When something isn't working properly, they want to be able to point fingers at someone and blame them. The vendor then blames someone else. Open source tends to be the polar opposite, which means huge red flags - hippie stuff, no payment, no liability, no pointy-blaming game.

Or so I've heard from people working in that sector. For places as conservative as them to deploy FOSS solutions, you'll need the government branches cooperating with clearly worded laws and regulations, dragging them kicking and screaming into adoption.

And that's assuming no one will lobby against in the process.