I agree with that. This seems like a great idea and I know what you mean about the hassle with OCTGN card packs. However, as a web app, you're perfectly positioned for a 'best of both worlds' approach. As soon as the six month are over, you can add the artwork server side and it will show up for everyone without effort on their part.
I think it's important, though, to realize that FFG holds the rights to this game. You'll only be able to pull this off with their (implicit) consent, so I think you have to make some effort to play by their rules. It's great that you want to create the best game experience possible, but please consider how FFG will react to that.