9 Month Season,
Starts off with slowest surface and ramps up through the season.
2 masters, plus 1 GS per surface over a two month period. So start of each month Masters, GS starts 2 weeks in to second month.
Go from Clay, to slow HC, to Fast HC to Grass (would prefer a 4th surface but carpet sucks).
YEC in 9th month, along with last masters, surface for both by vote of top 8 players, weighting vote by ranking, i.e 1st rank worth 8 points, 2nd 7 points and so on.
Bigger differences between the surfaces in terms of speed, bounce etc would be a must too so that more variety of play is present. (S&v back in the day wasn't good despite what the oldies keep saying. Everything from racquets, to conditions favoured it and thus the net player, now with new string and racquet tech i think it would be balanced even if you sped some of the surfaces back up, and besides slower courts surface would still favour baseline, faster would favour all court/net play.) This would provide more variety in who is successful and what styles of play would be present.
The increase from slow to fast would allow players to adapt to different speeds and the footwork requirements of different surfaces so you wouldn't get the 15 injuries you seem to get at Wimbledon these days.
Time off would allow players to develop more.
The other tournaments would be played by lower ranked players creating a more sustainable scene for those ranked outside of the top 100.
Not very practical but probably ideal for the reasons above, however good luck moving surfaces and tournaments time slots etc with people who cling onto something significantly less optimal for the sake of 'history'.