As I and a few others have been saying for over a decade now...
Reduce the Prem to 8/10 teams, with another 10/12 in the Champ - ring-fence between Champ and NL1.
Replace the AWC/PC to include all 18-22 English clubs; in an orthodox format (with Cup, Plate and Bowl finals for extra games); with the prem clubs limited to no first XV players (anyone who played >60% of the previous season). Play that domestic cup competition during all international weekends. Split Sponsorship deals more evenly between those top clubs; with a TV deal that necessitates coverage of the championship.
Boosts player welfare, as the starters are given rest weekends; and gives the backups a chance to challenge for a place.
Boosts the quality of the prem by cutting any deadwood there is to cut.
Boosts the quality of the Championship by replacing 4-6 poorest quality clubs with 2-4 premiership quality ones.
Reduces the impact of relegation, protecting investment, by introducing ring-fencing (just not at the level the top 12 clubs want).
Boosts income for the Champ by adding TV coverage (and consequent sponsorship and fan-base), adding big-name opponents to the league, and adding giant-killing opportunities in the cup.
The only cost is game-time for the first XV; but there is simply no way to reduce game-time which doesn't include a reduction in game-time. This is a good thing for everyone except the club owners, who really ought to see it as a good thing as well; they've just proven that they don't.