I think it will, at a minimum, further keep teams from drafting safeties, guards, and running backs in the first round. They want that low cost fifth year, and so to maximize value, you want that low cost fifth year on positions that are expensive on the FA market. So pass rushers, left tackles, and QBs will go high. "Low cost" is relative. It's basically a franchsie tag in year 5. But it's pegged after year 3, not year 4. Also, the team can use the tag in year 6 at the non-120% rate. No extensions are allowed until the end of year 3, and a team has tons of leverage over the player, b/c they can control him through his 28th year
This really has the effect of benefiting good teams. They get the fifth year cheaper than the teams picking in the top 10