Agree with this. If you can't intentionally queue up that way, then league should not be capable of matching you that way.
The argument against this is obviously: a Gold 2 queues with a Plat 5, and a Gold 3 queues with a Silver 1, and that Gold 2 and Gold 3 get put in the same game. Voila, a Plat 5 and Silver 1 are now in the same game. However it doesn't make sense to queue that way, League should be queuing better than this.
Also, a Plat 5 could theoretically have as low as Gold 4 MMR without demoting (you need to be a full tier down to demote is what I've read). A Silver 2 could also easily be Gold 4-5 MMR. So the problem yet again is why MMR is allowed to deviate so far from actual rank. Stop protecting the boosted animals from demoting (maybe increase the protection at season end so people don't stop playing for fear of losing their ranked rewards, but otherwise let a Plat 5 demote when they hit Gold 2 MMR...). Also let people climb a lot more easily (whenever you win a promo series go directly to the division of your MMR, not just up 1 division or skip a division if you're 4+ ahead). If you promote from S4 and are going to be playing with S1s, then that promotion should put you in S1 or at minimum S2, not just normally to S3.