My vote would be to meet in the middle and have the best of both worlds. Grand Campaigns like we have now which go from Tier 0 to Tier 5 (1940 - 1945) which after there is a victor would be followed by a short intermission, which would then be followed by a time limited (5-7 days) mini-campaign with set victory conditions placed at some point in history (i.e. Operation Market Garden where you begin with Tier 4 weapons). After the mini-campaign is over you would do a short intermission and then follow with another Grand Campaign.
This would have the benefit of allowing CRS to experiment with late-tier equipment balance or small tweaks to capture mechanics, build times, etc. since the mini campaigns are only for a week or less.
Interesting scenarios I could envision for the mini-campaigns:
Defense of Paris
Invasion of England
Invasion of Crete
Seige if Tobruk
Battle if El-Alamein
Invasion of Sicily
Normandy Invasion (immediate post landing push on Caen)
Battle of the Bulge
Battle of Hurtgen Forest
Fall of Berlin
Ypu could then add any number of hypothetical what if scenarios. Such as a Tier 1 where France doesn't fall and Allies are pushing across the Rhine. A Tier 0 where the Acis land inEngland and push to capture London before the Anericans who are now forced to enter the war early can rush in an army to help the British.
EDIT: The above wouldn't take the place of special events, rather it would be for scenarios that take more time than a few hours that special events take. Or scenarios that are more combined arms in nature vs. special events that are more geared to one branch (i.e. Channel Dash, Defense of the Reich, DamBusters, Pearl Harbor).
Grand Campaign: Weeks/Months
Mini Campaign: <7 Days
Special Event: Hours
The major benefit of the mini campaign is that it gives players the chance to start with 1944 equipment, or similarly have a short campaign only with Tier 0 tanks when we are all fed up with Petshings, King Tigers and IS-2s fighting it out.
It also gives CRS the chance to experimenting with new gameplay mechanics on the live server. So we could for example see what would happen with shorter capture timers, or any number of tweaks.