The main issue as I see it is that the have one server cluster servicing the entirety of the united states, canada, and other countries.
You can't have literally millions of people playing on the same set of servers without having MASSIVE issues, even beyond just ping.
They need to split NA up, the server load on NA is just too high to be sustainable, and with LoL continuing to grow in size, I don't know how long the NA servers are going to be under this incredibly heavy load.
Let's look at some facts: ping, especially for the east coast, has been steadily increasing for years now. The NA LoL player population likewise has increased.
Now, i could be wrong, and this particular correlation could not be the cause, but the fact that as the game got bigger, the lag got more problematic seems incredibly significant to me.
They need to split up the server traffic, lighten the load so to speak. Almost every other area has multiple servers. SA has LAN/LAS/BR, Asia has about a bazillion servers, Europe has 2 or 3... But North America, despite having a pretty sizeable group of LoL players, only has 1 server (NA.)
I think that Riot's stance of being cautious about splitting up NA is no longer valid, that they need to split NA up so that the servers aren't constantly fucking up due to the incalculably enormous amounts of traffic it has to handle.