Basically the point here is not to only remove the Tiers, but improve instead and we all know that "Tier 2 and Tier 3" is not for everyone, so the idea is to make this a more comfortable way for the Views to use it and for the Streamer to manage!?

1° Instead of the "Tier" the sub should be a fixed price.

2° Add an option that make viewers choose if they want to pay more for the sub and that extra being like a donate.

3° That would be an way to not have a separate "Donate Button" on Twitch Channel and since we all know that twitch is good with "payment methods", adapting this to the streamer region would not be a big deal.

4° Twitch should discuss this with the community about the "share and tax" for the streamers.
E.g. If this idea get implemented on the way that sub it's right now, people would be mad at the share they would receive from it.

5° The Reward/Prizes for "Paying More" should be on the hand of the streamer to choose the amount and be creative with it.
E.g. "Channel Points Buttons" exclusive for it, the "Tiers emotes" and a lot of things.

PS:. In the end is just an Idea having in mind that is not perfect, would be an improvement at least to me, but feel free to add any extra suggestions on the comments.