Ideally, four weeks of grass-court tennis before Wimbledon. First week has two 500s, then two back-to-back MS1000, then a week of 250s in the week right before Wimbledon. This would give a similar run-in as RG & USO.
Alternatively (because the world isn't perfect), one week of 250s, one of 500s, then an MS1000, then the week of 250s. (I.e., insert a masters into the grass season after Queens/Halle.)
A few questions to address:
a) Capacity to enable a MS1000 event. Queens & Halle would be the most natural choices, but from what I have heard (?) neither might be able to support the required numbers.
b) Cost of maintaining grass courts (often quoted as a reason for the reduction in grass-court tournaments).
c) The extra week must be found from somewhere else in the calendar.
d) Some masters tournaments elsewhere would need to be scrapped / downgraded.
It seems to me that it should be possible to solve a). For example, if there is only one new MS1000 event, could it be at Hamburg, which used to be a Masters. Admittedly, somewhere further south might be better weather-wise. In any case, it seems there would be solutions if the desire was there to make this happen.
I don't know enough about b) to comment. But current grass-court tournaments seem to be managing, and other sports are played on grass also. (Admittedly, quality of the grass may be less of an problem e.g. in football where the pitch is so much bigger, and fidelity of the bounce less of an issue.)
As for c) and d), here is a possible solution: Get rid of one of the three clay-court MS. E.g., change Madrid (weird tune-up for RG anyway due to altitude) to a 500, move it parallel with Barcelona (so two 500 in the same week), stop one of the current clay 250s in that week; have Monte-Carlo be the second (compulsory) clay MS.
The issue with this suggestion is that we would end up with 9 or 10 compulsory MS events, whereas currently there are only 8, and the calendar is pretty full as it is. But there would be some nice symmetry: two MS associated to each of the GS, and 2 for the WTF.
The other thing is that we are taking away from clay instead of grass, rather than reducing the amount of HC tournaments in favour of the natural surfaces. But the only other choice really would be to reduce the North-American hardcourt season, and I am not sure that would be too popular.
Any thoughts?