Primaris Space Marines are not designed as replacements for existing Space Marines; they can either be fielded in their own Chapters or integrated into existing Chapters. And although they’re stronger, they will also cost more points than standard Space Marines so won’t be practical as a complete replacement for them.
Kits will be somewhat compatible with older ones, although some parts of the new armor aren’t cross-compatible.
The initial reveal, pictured here, is an Intercessor wearing Mk X Tacticus armor with a re-engineered, re-crafted and perfected bolt rifle.
Two other reveals from the announcement: a Primaris Redemptor Dreadnought is planned; and the release date for the new edition of Warhammer 40K will be revealed before the end of the month.