Hiro 4 will be to M4, what Aiko 4 is to V4.

From the Hiro 4 News and Wishlistlist thread:
http://forum.daz3d.com/viewtopic.php?t=95790&highlight=

What we know about Hiro 4 so far:

http://www.daz3d.com/i/3d_models/overview?_m=d wrote:
Hiro is the popular male counterpart to Aiko, the most sought after 3D anime female in the world. Hiro 4 is currently being developed based on the Michael 4 base product and will inherit all of the latest improvements of the 4th generation of Millennium Figures. Stay tuned for more info on Hiro 4!

1. Hiro 4 will be a morph of M4 (similar to Aiko4/V4)
   Hiro 4 will be released as a separate figure from M4

2. Hiro 4 and M4 will be able to share clothing and hair.
   Requires the Hiro 4 morph in M4 clothes, and the M4 morph in Hiro 4 clothes

3. Hiro 4 will be as tall as M4, not shorter.
   Similar to how Aiko 4 and V4 are the same height

4. Hiro 4 will be able to share texture maps with M4, A4, V4, and V4 Male.
   However, the alignments on areas like face will be off. Use UTC2 to convert textures between figures, swap V4's UVmaps for M4's, or use M4 Enhanced for correct texture alignments between V4 and M4

5. Hiro 4 will be able to share morphs with M4/A4/V4/V4male
   But transferred morphs may not look the same because the default shape is difference between the figures. M4 Enhanced will correct V4 morphs transferred to M4 so that will look correct.

6. Hiro 4's known Full Body Morphs are:
   Hiro Body
   Hiro Stylized
   Hiro Sylvan