The Collection will include the first three games, as well as other extras.
http://www.nintendoworldreport.com/news/27016
Square Enix will release a compilation of the first three Dragon Quest games on September 15 in Japan. The compilation will include the first footage of Dragon Quest X, which was originally announced for the Wii more than two years ago.
The collection includes the first three games in their original Famicom form, the Super Famicom remakes, and a few extras. The extras included will range from a reprint of the original game guides, a recreation of the series’ “Small Medal” item, an art collection that will be included on the disc, and brand new anime intros for all three of the games.
There are currently no release dates for the collection outside of Japan.
The reason this collection is unlikely to be released outside of Japan (even though I would buy it) is because the SNES remakes were never localized, so they they would to do that with all three games. This collection likely would not be a huge seller outside of Japan, so they may feel it's not worth it. Anyways, the preview of Dragon Quest X should help boost sales.