Developmentally 6-10 is too wide of an age spread for the very young kids. I currently have a little one turning 6 in September, and I think a MINI is very appropriate for her (8 and under as it is currently). 9-10 year olds are a lot more mature than kids just entering into first grade, so I would not be fan of trying to lump them all together. I would want to continue with a Mini, Youth, Junior and Senior. Also, she is only 5 right now and misses the age cut off by 3 days--but she has multiple back handsprings and fits great with a mini 2 group--since there are a lot of 5 year olds in her position (late fall birthdays but still going into 1st grade) I would be an advocate of 5-8 for minis IF a lower age limit was placed on this.
I would support moving the lower age to senior of 13 and having it "overlap" with Junior. But, moving it to 14 period does not allow gyms to make the decisions they feel best for their individual kids. I am personally a huge fan of Junior level 5 divisions (our gym has both a Jr and Sr Level 5 team)--but there are some kids definitely better suited for Junior and other better suited for Senior (mostly the kids who have been doing this for 7+ years already).