I honestly don't think it would be very fair. There are people who have been waiting a year for toys (even silicone!) and bumping them further back because someone who has been waiting three weeks bought the brand new rush seems wrong. The guy waiting a year for one silicone toy deserves priority because he came first. If there was no backlog at all, this wouldn't be a problem, but there is a backlog and those waiting a long time should have first priority.
I also can see this creating two different backlogs out of the current one; one of "rush orders" and one of people who will be waiting a lot longer as the rush orders are going to be going first. As the current backlog clears up, I agree with erythro: there's a chance everyone will start buying rush to not be left in the back of the que.
I also am concerned that people who don't order rush will be put on the back burner for a long time, leading to more people upset they waited a year for a single silicone toy and more refund requests and complaints. Hearing "Go buy rush" (even if from a well-meaning forum member) when you waited a year for a single toy is not going to keep people happy. If anything, it sounds uncaring and money-hungry.
That. I see no good coming from this. Only more backlogging.
If you want something like this, make sure you're completely up-to-date with the current orders. As in, waiting time max. 6 weeks in ALL cases. Until then, there's a backlog and this plan will only cause a lot of frustration and angry customers. And they'd be damned right.