For our family it's always been a concern and it's why my daughter is a Y gymnast. She now trains 4 days a week, a total of 14 hours, but that is only as an optional, prior to that it was 3 days, 10 hours total. So she still trains under the norm but it is enough. She is a burn the candle at both ends kids so this suits her well. She works very hard in gymanstics, but she also has a very active social life both in and outside the gym
She plays field hockey on a club team and she played soccer in middle school for 7th and 8th grade. She used to play travel soccer but she quit because her team became very demanding with tournaments and practices and there were always gym conflicts. Field hockey was a trade off because it is less intense. We know ahead of time when all practices are and when all games are (scheduled day of week). She also runs track at school, as does almost every gymnast at her club, but even a lot of club gymnasts seem to run track around our area.
For us it was important that she not spend all her time on gymnastics as a young kid. We figured as she got older if it was something she wanted to stick with as her one and only it would be her choice. The flip side of that is the chance of that happening decreases every year when you are at a program that is good but not great. So the time to make the move would probably have been younger. She has been torn sometimes but ultimately she likes the flexibility to do other things. She is really looking forward to highschool to participate on either the field hockey or soccer team.
Our other children are boys and we have only been involved with sports such as soccer and basketball and to some extent swimming. Her brothers all played and play highschool ball and we felt they benefited from that immensely. Our oldest plays D1 soccer and my other son seems to be headed in the same direction. And while they played a lot of soccer in order to get to that point, the intensity didn't really pick up until 9th grade and much of that was school related. They were able to play other sports and be competitive.
The difference here is that she will more likely not be a college gymnast (it's really not even a goal at this point) nor will she be a college player on another sport unless she really gave up gymnastics. Time will tell.
I do think things are different with many sports though these days than how they were with my oldest. Now it seems every damn soccer team out there calls themselves elite, and the intensity is so much more. Seems to be the same with every sport.