AI is used worldwide. Despite PostScript, based on points, based on inch, being de-facto a standard for most users, many people use metric system.

English inch, as you know, equals exactly 2.54cm.
This gives us, metric users, mantra for translating PPI into PPCM: 254ppi=100ppcm

Since fractional values for resolution are impossible within AI (while Photoshop does!), we have to import via PS or work in scale and are very limited.

Please, add ability to use PPCM along with PPI, as Photoshop does.