"Fast lanes" as a general product aren't likely going to be offers on the company home page, they're going to be in the private peering agreements they have with larger companies. This has already happened. [Netflix had to pay Comcast](https://consumerist.com/2014/02/23/netflix-agrees-to-pay-com...), and [Comcast throttled their VoIP competitor Vonage](https://www.wired.com/2006/03/comcast_throttling_vonage_user...). Vonage and Netflix started working again but the why was never made public. It seems likely that paying for fast lanes was involved. These aren't the cold hard facts we'd like to have about what exactly happened, but they're clear violations of Net Neutrality that were resolved ambiguously.
As far as negative effects in general, beyond fast lanes, there's more than a few examples:
* [AT&T blocked FaceTime](https://www.savetheinternet.com/att-facetime) * [Verizon blocked Google Wallet](http://money.cnn.com/2011/12/06/technology/verizon_blocks_go...) * [Verizon throttles video](https://arstechnica.com/tech-policy/2017/07/verizons-throttl...) * And [a lot more](https://www.freepress.net/blog/2017/04/25/net-neutrality-vio...).
The violations are often subtle, and haven't always affected everyone, but the negative effects of the lack of NN are not hypothetical.