Honestly, I'd expect Apple to drop S3 from the model table when S4 or whatever they'll call it premieres just like they did with S2 when S3 launched, to not have two fairly similar specced and priced models for sale at the same time. If they don't, a lot of potential S4 sales would instead be cannibalized by S3 sales.
If I was to speculate further, I'd assume S1 would remain as the low-end offering, kind of like iPhone SE have been for a while now. There isn't much room for S3 to move down in price due to the much higher specs of that model; if Apple cuts S3 price they'll just cannibalize more S4 sales and their ASP/revenue would drop. If they don't drop price (much), the high-end of their model offerings gets cluttered by two similar-ish models, and there would still be cannibalization going on.
Of course, I could be wrong. Maybe Apple only drops the ceramic/stainless/LTE versions of S3 plus the old S1, and keeps the aluminium, non-LTE S3 as the new low-end model, while the new S4 models will be greatly upgraded and provide a significant feature, performance and functionality difference... *shrug*