The game is moving in this general direction, there are two hindrances impeding this change.
1) Limited roster spots - rosters would need to be expanded to accommodate the extra pitchers teams would need to really pull this off.
2) Lack of talent - While teams will be using their pitchers in a more impactful manner, this comes at the cost of needing to give more innings to worse pitchers who previously wouldn't have been pitching. The real question is where does the balance point lie. If the impact of shorter outings is greater than the drop off from the last guy in the pen to the first few guys at AAA, then we could end up seeing this.