So I was setting up some seasonal sales after getting the sale reminder e-mail. But while setting them up, I noticed there aren't any options to customize the sale page, the way one would for a store page. 

It would be nice to customize to either make the sale page cohesive with the game pages or to add sale specific graphics, like seasonal backgrounds for seasonal sales. Autumn leaves, snowy drifts, icicles, hot cocoa, flowers, rainy streets with umbrellas, sandy beaches, that sort of thing. Being able to overwrite the sale title with a thematic banner would be great, too.

An option to copy the page customization from one of the games/products included in the sale would be amazing, as it would save people time making all their pages cohesive. Font, bg image, colors, etc could all transfer over. The left hand side of the sale page could have identical settings to the game page, and the right side could have a darker/lighter bg. 

Tangentially, could we have a setting to schedule sale visibility? Right now the only way to keep a sale private until the start date is to keep it a draft, but I'm prone to forget to come back and set it live.

Ex: Dev wants to have a simultaneous sale on itch.io to coordinate with other storefronts, but the dates of the sale on other storefronts is supposed to be kept private until it starts. If there was a third setting besides Draft and Publish, like a "Schedule" setting that would go live either at the start sale date or a customizable Publish date, then a dev wouldn't have to worry about agreements with other storefronts.

Thanks for the idea. I don't have any immediate plans for making the sale pages customizable but I think it's an interesting idea. The hardest part about customizable pages is that they're complicated to maintain. We try to make pages look good & work across as many screen sizes but for pages that have customization parameters (especially custom CSS), it becomes a lot trickier. I'm in the process of re-doing the game page theme editor and afterwards I can see if what I've done can be mapped more easily to other pages.

Regarding the publicity of sales and when they start: at the moment we don't show sales that aren't active anywhere on the site, so if you publish a sale then no one would find it unless you share the direct URL. That said, we don't tell people that's how it works, and I don't think it would be unreasonable for us to have a future sales calendar at some point, so I think adding functionality for scheduling would be good.

Oh cool, sounds good.
Thanks for the info about sales, makes my life easier to set and forget, haha. When you get around to sales scheduling, it might be nice to have it integrate with the tool that e-mails prior customers, to say something like: "game you liked is on sale, maybe tell your friends to buy it, share sale link, etc."

Have you seen the sales management page for Humble? It has a good selection of features.