I think remakes made sense with FR/LG and HG/SS, but I'm not so sure about RSE. Kyogre, Groudon, Rayquaza, and the Gen 3 starters are obtainable in HG/SS, and Diamond and Pearl had virtually every Pokemon in existence up until that point, except for the starters and legendaries from older games.
If they do RSEmakes, I'd rather they have plenty of new content. Mix in some of the stuff from Emerald (battle frontier, for example), maybe expand the postgame even further with a Sevii Islands like area where other Pokemon can be obtained. Give us the chance to get Dialga, Palkia, and Giratina, because they're getting harder and harder to obtain.
As for E3, I'm not sure what kind of announcements we'll get, or if Nintendo will go back to a traditional presser or stick with the Nintendo Direct format from last year.