Ok, so after digesting this topic for quite some time (about 15 minutes), I have come up with this idea:
In order to keep the GM's participation up there are a few factors to consider. The first is the timing of the league start date, every SIM league I know has fluctuattions in involvement but the summer months and Christmas are the 2 that stand out as times of the year where GM's aren't very active.
If the plan is to have 2 full seasons per year than they have to be scheduled around summer and Christmas vacation. So, my proposal is that the seasons start after New Year's day and end by June which gives us 5 months to complete a season and conduct all the essential items for the off-season.
The next season wouldn't start until September 1st and conclude the 3rd week in December or around there which, unfortunately only gives us 3 1/2 months to complete the season but we could bypass the all-star break and wrap things up more quickly.
Now, if those timelines are sufficient enough or they need tweaking that's no problem, at least we have the basis for a general timeframe.
To keep participation up, my idea is rather simple:
1) GM's must submit lines every week or ask for auto lines during periods they are not available
2) GM's must respond to league-wide polls, trade offers and a GM roll call to remain in the league
3) A point system be introduced and maintained and those points be used for various things such as Arena upgrades, sponsorships/endorsements etc.
4) Weekly winners of participation points but the same GM can't win every week...that needs some tweaking but hopefully you understand the reasoning
5) When a GM is recruited, he/she must agree to the new rules of the Participation Points Award Program (PPAP) or face the possibility of fines, player suspensions or eventual dismissal and a ban from the NASHL
The NASHL is a SIM League that needs GM's to be active in every sense of the word...if you look to the left of your screen you'll see the top posters, we need everyone to be over half, to stay viable and keep the league afloat.
I believe that with a scheduled vacation break we eleviate the possibility of huge swings in participation and thus increase the viability of the NASHL.