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.