I personally have no problem with this at the U10 or possibly U12 level provided it is fair for all participants. In fact they've just introduced a national U10 teams competition in Australia that does this. They take the best 32 kids in each state, place them in teams of 4 each with a designated coach and play a round robin tournament over 5 weeks to help choose a final team of 4 boys and 4 girls from each state to compete during the second week of the Australian Open.
The format for each tie is 50 minutes of continuous singles, 10 minute break then 50 minutes of continuous doubles. Some kids ground away and barely completed one set during the time while others were beaten 6-1, 4-0. During change of ends the designated team coach (not parents or regular coaches) could take the kids aside and talk them through possible strategies and matchplay.
It worked very well and because the make up of the final team isn't based purely on results, there is no disadvantage to kids who needed little or no coaching because the coaches know who they are and I imagine that actually counts for them.
Sounds like a wonderful idea. We need to incorporate the (fair) coaching opportunities more in the young players' match play here in the US.