> Let's see which tech stack and which customer support organization survives the merger, respectively...

I have no inside experience of either company, but I have been through a lot of large financial industry mergers and I know what's public about this one.

I'd bet heavily that it'll be some of both, but tech especially will be Capital One. Because it's larger, because it's the acquirer, and maybe above all because it's newer - a younger company with a younger tech stack that's known to be entirely cloud based.