At any rate we'll know for certain if this is bad internet rumor or any truth to it at all come October 14th...or sooner.
Assuming it's true for speculation sake though it would be possible to have Silver Surfer show up maybe in a post credits sequence. In some 20-30 second spot he mentions how Thanos use of the Gauntlet has triggered Galactus' interest and he wishes to help them stop Galactus from getting to Thanos and/or The Infinity Gauntlet. Something.
Then later on in the MCU we could get a good solid solo Silver Surfer origin movie since the cosmic side is firmly now set up. Remember SS was SS long before he showed up on Earth to tangle with the FF. No reason a solo movie sans FF can't happen. Would be awesome to see Airwalker, Terrax or Firelord realized on screen!! The In-Betweener!!