You send 750 BTC to MP now and someday later he will send you 1000 Gavincoin back.
Which means that you pay 750 MPcoin in exchange for 250 Gavincoin.
(Unless the 750 BTC is also "future payment", after the fork, but then he should say it more clearly)
Unless MP is firmly linked to a real-world identity that can be held legally responsible for non-performance, and I personally can prove in court that the counterparty on that IRC channel has the same legal identity, I will not be paying MP, over a fuckin' IRC channel no less, for any promises of any kind.
Come on, guys, we aren't supposed to be idiots. Why would we deal with anyone via an unauthenticated protocol for future performance or delivery of anything?