It seems like it would be the first time someone has done it properly. What is so beautiful about Twilio is their attention to detail for developers - amazing documentation, samples, etc so I am assuming their MMS implementation will be as clean. Here's hoping.
mBlox, OpenMarket, Mobile365 all tried to implement the half assed MMS implementation forced on them by the carrier market and it was an absolutely nightmare. I'm surprised noone in the tech press ever did a deep dive expose on just how archaic the whole certification process was, and the user experience was terrible.
Summary: this is not the first time the carriers have opened up MMS. Hopefully it will be the first time developers can leverage MMS the way it was intended.