Boots should be automatic and in their own slot, like a trinket.
What is the point of having them be optional?
In the vast majority of games (not those that go on for an eternity in which you can swap out boots for zephyr as an adc or something.), boots are mandatory anyway.
The point is if RIOT expects everyone to buy boots at some point, (including new players who don't really know that boots are considered mandatory in real games) then why not just make it its own little slot like a trinket, to improve clarity. Your first pair of boots is free and doesn't grant movespeed, then you can upgrade it to brown boots and upgrade it again to the second tier boots of your choice, and you can still put an enchantment on it if you wish.
If people are worried what might happen if there is basically a whole additional item slot, then remove one slot or adjust itemization across the game for the new slot.
were automatic, their existence would be pointless. Riot could just add +25 MS to every champion's base movement speed, or not do anything and still remove the basic Boots of Speed. Almost everybody always picks up boots, yes, but not everybody and not always. It's a strategic purchase to gain an advantage or help even the playing field. Some people even drop boots completely in their full build for less MS and more damage.