I absolutely LOVE the design. Personally speaking though, I'm not sure that I would use it (unless I had a really good reason to) because I tend to be quite apathetic that way. Maybe apathetic isn't the right word - I seem to get swamped with various things going on in my life, and I don't know that I'd have enough time or attention span to do this - unless I was sending another Steemian a present maybe.
There may be other more focused Steemians who would take up this idea though. And maybe if it took off, then I would join in too :)
I suppose if I was to suggest a way to improve it, I would say, present some situations where people would send steempostcards, to catch people's attention and get our imaginations working!