As rumors become future news in regards to the impending increase in roster size (to 30 total players). There is much rejoicing in MLS fan land. Immediate excitement breaks out. People are thrilled that there will be larger rosters. Some excitement exists due to the likelihood that this change expands the HomeGrown Player Rule.
But while there is speculation that this rule change is due to the larger schedule for next season (34 games), or due to Don Garber "wanting to be more competitive" in CONCACAF Champions League, that just isn't the case.
The Seattle Sounders would not be doing better in the CCL if they had four more players at the level of skill of Miguel Montano and David Estrada. Is having a 2nd Tyson Wahl on the roster going to be a help in Game 33?
Without an increase in the salary cap for these additional slots, they are just adding to the size of the roster. Nothing changes, unless said player gets sold in a transfer later. The effect on the league, and its related games will be minimal.
If this is purely additional Home Grown Players that won't raise the skill of the overall team in the short term either. Likely it won't effect the long-term as well. Because if the players aren't playing, they aren't playing. So if the additional roster slots are really just a way to get off-cap players (HGPs are cap exempt, but generally low salary and coordinated with Adidas) onto the Senior Roster, but playing in Reserve League games, that is a good thing.
It would reduce the number of older players on Reserve contracts (~33k$), and have the Reserve League be a league of primarily players who are climbing the ladder, not just a stockpile of the same old problems.
In the end, the change is a positive, but not a dramatic one. MLS teams won't win the CCL because of this. MLS teams will not have a dramatic talent improvement due to this change. The biggest change is that nearly 100 more people in the US and Canada will be professionals. Not just people paid to play, but people for whom their entire life is the game.