Honestly I think that's what the leveling system accomplishes to a point, and while I'll admit it's a bit of a rough transition from 29->30 before then you are paired up with <30's. As for competitive playstyles, isn't that what ranked vs. non-ranked is for? Granted I realize the more competitive scene mixing with the casual crowd being a headache for both sides I feel it's more of mistaken intention in que, normals is for casual play and ranked is for competitive. If a competitive player has a problem with a casual player having fun in a normal then it's his/her fault for expecting ranked behavior. All imho, and I admit it's something too many people don't realize this.
This unfortunately will not stop smurfing and in fact would inflame the issue, giving smurfs a literal 'target group' to que with. Smurfs are made to either a) play alongside a new player or b)(Most commonly) to **** on new players. Giving a 'focus group' made for new payers would be like a smurf candy store.
There is also the danger of 'fracturing' the community if you seperate ques. One section will naturally be much more popular than the others and thus the smaller groups will have a serious contrast in numbers. If even one of these splinter groups is too low you wouldn't have the numbers required to havea good matchmaking experience.
Tl;dr Rankd and normals kind of do this already, although it can be made more clear. Dividing the community in any way (even dominion had an issue) is very risky
