The only thing good about this ideal is that it is harder for an afk asshat to hide in 9 people than 24.
The problem is that dps AND HEALER queues would go up. Currently the system attaches 2 tanks to 6 healers and 17 dps, under a 10 man system it would attach 2 tanks to 2 healers and 6 dps. That means currently 2 tanks carry 23 people into LFR but this system would have 2 tanks carry 8 people and 14 people would still be waiting for 2 tanks per potential group. Tanks are a tiny resource.