I made reqs about a week ago, and when the test first started, I was definitely in favor of banning Landorus-I. Like many others in this thread, I thought its ability to u-turn into Tyranitar as soon as Celebi or a Lati switched in completely broke Landorus, and I was sick of seeing the same basic core in nearly every match I played.
However, after testing Landorus for myself, I’ve started to change my mind. While u-turn is certainly useful for getting rid of Celebi and dealing with stall, I think the life orb damage really hampers its usefulness in the long run. While it is true that u-turning always allows you to keep momentum, I believe you also have to consider that you are taking 10 percent in life orb damage plus damage from stealth rock whenever you switch it back in. Furthermore, when you consider that Landorus-I is already pretty hard to switch in with all the scalds, ice beams, and strong neutral attacks being thrown around, I found that when I actually got Landorus into play, I usually didn’t want to risk taking it out again unless I was absolutely certain Celebi or a Lati was going to switch in. While I guess you could run expert belt or something instead of life orb, I feel like you would miss out on a number of important kills (I don’t have calcs or anything to back that up though).
Additionally, while I do agree that rock polish is deadly, I personally found it hard to set up, and I think that Terrakion and Keldeo are both better late game sweepers right now.
In regards to the stall argument, I definitely agree that Landorus can give stall teams a lot of trouble, but I don't think that banning Landorus is going to make stall much more viable than it is now. Keldeo with Tyranitar support and Kyurem-B with substitute can both be just as effective as Landorus-I against stall teams, and I don't feel that any one pokemon is single handedly destroying stall's viability at the moment. In fact, some of the best teams I saw on the current ladder were stall teams.
Granted, I might have been using Landorus incorrectly, and someone could definitely change my mind in the next few days. However, based on my experience, Landorus-I is not overpowered, and I plan to vote no ban.