The harsh winter weather in the northeast, midwest and Canadian cities during January, February and even most of March does not allow for the fields to be in the best of conditions for the start of the season. Also, fields tend to hold up much better in November and December than in the Jan, Feb and March.
The league should look into starting the regular season 3-4 weeks later, in late March or early April. The regular season could end in November on the last weekend before the November FIFA match date. Playoffs would then start up after this and the MLS Cup would be played the weekend before Christmas.
The season could look like this:
Jan - Offseason
Feb & March - Preseason
Late March/April - Start of regular season
June or July - League takes 2-3 week break for Gold Cup, WC, etc.
November - End of regular season on weekend before FIFA match date
November/December - MLS playoffs and MLS Cup