This Stargate RPG looks like it might be a fun one, and hopefully it proves to be successful, although there are concerns about some of the decisions that have already been made and that might be made prior to its release.
With the introduction of a new race that was not present in the original movie or 3 shows, along with a number of other elements about this RPG, this game is a split continuity. It might help to market it as being part of an alternate universe so fans are aware of the differences. If anything, it could help soften the blow for those expecting something that could have been more true to those productions.
It sounds like this is based off of season 6 of Stargate SG-1, which is a great part of the history, although it would be nice to have the option of choosing any time. Time travel is an important part of the franchise. If anything, this RPG can start in the present, then travel to that point in the timeline, while still allowing characters to travel to the future or past. Of course, some or many players may do that anyway. Might as well write it in.
At the core of it all, however, Stargate has always been based in the present - that is, the present at the time of the production - so basing this RPG on the past, while rehashing memorable elements from the series can be nice, is just another step away from the foundation that the franchise was built upon. Starting the story out in the present day would at least be a way to maintain some of that foundation.
Earth is and always has been home. Sure, the shows took place in other locations - Atlantis in Pegasus, Universe across the universe - and those other places even become a "second home", although they always started on Earth. In most of them, they even returned to Earth. This is based on Stargate SG-1. Earth is home. The Phoenix offsite location can fit nicely into this, if it is simply that: an offsite location.
Considering how significant of a presence the Tau'ri have with the entire franchise, it would be a grave mistake to exclude them, enough that it would likely result in sending many fans away from this game, with Wyvern losing money, and Stargate fans spending their money on other RPG sources, opening up to different rulesets that may be more fitting for a more authentic Stargate RPG experience.