What in the rule changes you listed "opens up more of the field"? I don't see it at all.
8 players have to be on the line
Only two can be back blocking plus returner
The space between the two blockers and the line is open. There are no players there
The two blockers have to cover that space in the even a kick bounces over the front 8
If they play up closer then they are farther from the returner to block for him
the success rate of onside kicks will likely go up because more teams will attempt them
Sean Peyton had a nice interview about it that you should find and read
He thinks many teams will attempt more onside kicks because he thinks the success rate will go up
The old way is impossible now without the running start, so teams will adapt and use different approaches