If he has a good year I think he'll demand a good contract extension. But I don't think he gets to bypass the 4th year of his rookie contract. I still think he has to play that out.
I would imagine it wouldn't be that common. But it is a time period where you should have extra cap space. That will be the case for Dallas this year and next. We pretty much have a QB free of charge.
If during the offseason prior to the players 4th season, the team and player negotiate a new contract, the focus of negotiations is on the 5 year period starting with the players 5th season.
The team is not going to "give away" that 4th year of the rookie contract.
Once the basic numbers are agreed upon, then the actual contract is a 6 year deal starting with the player's 4th sesson.
The pay for season 4 could be identical to the original rookie contract or it could be any other number.
If the players receives a signing bonus immediately, then 1/5th of that will count against the 4th year cap.
The signing bonus could be delayed until the following March and then would count zero against year 4.
There will be a set amount of guaranteed money in the contract. Even if the bonus is delayed until the following March, the money is guaranteed. Other guarantees can be scheduled to be paid later.
The incentive for the player to sign early and not wait until the end of year 4 is that the guaranteed money is locked into place. A career ending injury in year 4 would still result in the player getting all guaranteed money.
A 2nd but much smaller incentive for the player is to get money immediately. For 1st round picks that have already made several million, it might not be a big issue; however, for a late round pick money immediately might be a significant incentive.
Scandrick screwed himself out of a few million dollars over his career because he wanted the money earlier than it was scheduled to be paid.
Scandrick is one of the only players I know of that took a paycut in order to get more money immediately. He did it a couple of times.
I'm sure other players have done what Scandrick did but he is the only one I know about.