The upcoming vision/ward changes
For me, I don't like the vision wars. I like that they're innovating on it but overall I think the most positive thing would be reducing the whole mechanic as much as possible. I've seen jokes on Elohell.net and stuff about how bronze through gold think support wards and then like plat and diamond think jungler and support ward and then challenger doesn't ward at all. It makes sense. Challenger probably has a lot of guys that have extremely advanced map awareness so they rely on wards less or not at all.
If I had my way, it'd be reduced to only the trinkets they're proposing or maybe even only the clairvoyance-like trinket. A semi-spammable clairvoyance would push players to have better map awareness (mistiming the usage you have every 'x' seconds could get you killed) and is both offensive and defensive. Wards just encourage passive play and I'm quite positive Riot is very against that.
Overall, I'm happy to see these changes and am curious to see how they play. The above is just how I'd feel vision mechanics could be changed for the best but I imagine most players disagree.
Edit (thanks to ploki122):