I love the idea. I have several friends that are eloping vs having big weddings due to cost and family strife.
I think that missing something is the chance you take when you decline to attend.
I did elope, in part to avoid the cost and the family drama. And I would do it again.
But an elopement is different than throwing a "normal" party, and then announcing that it's your wedding. Obviously I would hope that by doing that, the B&G wouldn't be offended by people declining. However, they also shouldn't be surprised that others feel hurt and left out because they declined a "party" and missed out on a life event they were otherwise invited to. For better or worse, it would make me feel less close to the couple, even if I was "supposed" to be there.
And yes, there is a difference in how I'd feel -- both inwardly and towards the couple -- declining a wedding I would love to go to but can't for whatever reason, and missing a wedding because I declined a "party".