Sure Sivir isn't the worst ADC at the moment. She still has a meh winrate, and is still Sivir so she's still really useful.
But overall she's come out of the preseason a little...lackluster. None of the keystones really work with her. Most people have noticed her feeling kinda weakish and her playrate has dropped by quite a bit.
My proposal is simple: Allow her W bounces to proc spell effects.
This would allow Sivir to proc deathfire touch with her W, proc thunderlords with her W, stack fervor with her W. It would also allow her W to proc rylais, proc spell vamp, proc liandrys, and other similar effects. But nobody plays AP sivir, so we don't care about that. Allowing Sivir to proc spell effects on her W would make keystones sync with her, and she would be a good ADC once more.