Proposals should be done in person, but lets face it, somewhere there are people who have "internet relationships" and don't want to really do stuff in person... so this is perfect.
.... Since we know that TF2 is Valves Experimental playground, I'm trying to think of how something like this could play into another game.
Just now I saw an alert of someone giving the ring to themselves. Or someone with an identical Steam name at least.
You know what this reminds me of? The "I Am Rich" app that Apple took off the iPhone App Store. Except if they had made it so everyone who owns an iPhone gets a text message every time someone buys it.