Here's the thing about Zepher, there's no reason to buy it if you don't count the tenacity. It gives a buttload of attack speed, but AS is a damage multiplier. It should be built after getting some AD for most champions. The tiny amount of AD from Zepher is not enough. You need a big ticket AD item first a lot of the time, to keep your power spike from being delayed. And even then, crit is just as important of a multiplier as AS, and there are multiple items that grant both. Zepher does not.
The CDR is nice, but most champions that value CDR highly don't value attack speed highly and vice-versa. A few champions do, but not a lot.
The movement speed is great, but if you want movement speed and tenacity you get these:
for much less gold investment.
Ultimately, the item is a mish-mash of different, random stats that may or may not be useful to any given champion. If the CDR was changed to crit to make Zepher an alternative to
then it might see some play. But that also brings up the issue that marksmen would have easy access to tenacity without sacrificing much of anything, resulting in a huge buff to their power.
You could go the opposite route and make the item more bruiser friendly by removing or cutting back the AS and increasing it's AD. But, again, you're giving a class easy access to tenacity without much of a sacrifice, resulting in a huge buff.
I think Riot is doing the right thing by removing it. Tenacity is a powerful ability that any class would love to have, but only tanks deserve to build freely.