Just some Ideas I think would work well.

1. You should combine the Heal and clarity spells Into a single spell.
2. You should combine the ghost and cleanse spells into a single spell making you immune to cc for the duration of ghost.
3. Clairvoyance feels outdated and could use a makeover in terms of utility so many items can do the exact same thing. not really powerful enough for a summoner spell. I feel this would raise the utility of the spells and make them something that people would want to use more often.

Next I want to talk about a couple of Items

1. the quicksilver active. Is a chore its awesome cause it can save your butt. The main problem I have is that by time I activate it I've already endured the gist of the disable. I think it would work great if you made it work more like the banshee veil passive. This also goes great with ghost combo I mention earlier making it great way to survive a cc heavy team.
2. The active like crescent, and the one on hextech gun blade don't really do much. Their hard to use, this means I'm paying out the but for something I'm not using and mess's me up in a team fight when I do try. Why not let these kind of active be ability mapped so they can be fired off in combination with a characters abilities automatically when they are available but still can be single fired if wanted.
3. also the grievous horn feels incomplete why not make a much better version of it.

Just some Ideas I though could really improve the gameplay of a already great game. and really bring it up to date since you all are making it over already anyway.