USL I don't believe has a salary cap so if MLS decided to expand in Sac there would be a number of players that would sign in the final USL season hoping to make the MLS roster. I think Portland carried over 6 or more USL guys, we are down to one now in our fourth season (two if you count Jake Gleeson who was USL Premiere (under 23)). If they get a move, tough luck. But you know, even Chivas has some great talent. Torres and Kennedy come to mind, Rosales may not be an all league star assist guy anymore but as a limited minutes guy is still better than you can do in an expansion draft.
But yeah, just putting things into perspective, besides the loanees, there are quite a few guys that were cut from Portland (when they sucked) starring for the Republic (RoRo comes to mind). Tons of player movement is just part of US Soccer. MLS is a selling league of sorts, even though we've brought in guys like Dempsey and Bradley the past two seasons, a lot of the "names" are at the latter stage of their career and a lot of the young talent moves on to Europe after a few seasons. It's just a reality that even if Sacramento makes the jump to MLS, if they develop an all world talent that talent will probably move on to bigger and better things outside the country at some point.
On the other hand, if you like the "player movement" threads for the NBA, you will love the global soccer transfer market
Portland has a guy on loan from Denmark - he was a 59 overall in FIFA (out of 100) just to say how "highly" regarded he was on the international stage - he's got 4 goals and 2 assists in 2 starts and a few subs. The ability to find unknown talent that lights up the stage actually exists at this level. And by the time Sac gets a team the salary cap should allow even more flexibility than teams have now - expansion teams don't necessarily start off at a huge disadvantage like they do in other leagues.