OK Riot - It's time to implement VoIP
You can't play team oriented games effectively without VoIP being included. Look at counter-strike competitive: I love that I can converse and make play calls to my team mates over voip. It also makes calling rotates that much easier and doesn't take me out of the game to type a message to my team.
Just because I'm not aiming cross hairs doesn't mean I should have to take my hands off the controls to voice some strategy to my team. There is a HUGE problem with players typing too much in ranked play often taking time away from farming or rotating for a team fight/objective.
You say, "but the pinging system is designed to streamline calls" well it doesn't do a very good job when most people ignore them or can't hear them above the music they are playing. Allowing a player to voice his strategy "Hey I'm rotating bot through river" or "Be careful mid is missing and was headed top" are things that will never be effectively communicated using pings. In order to get that message across I need to type while en route and nothing guarantees my tunnel visioned team mates will even read the chat to react accordingly.
The only fix is to implement a VoIP system in league to assist players that are complete strangers communicate in a game they are expected to play in collaboration with each other. Do not fear trolls just find a way to contain them. Making muting as easy as Tab+Click is a fantastic place to start. The bottom line is that professional and skilled plays come from team cooperation over VoIP. Without it solo queue is doomed to more missed opportunities because low level players don't know what to pay attention to and higher skilled players in those queues have no way to help these players excel.