Well, having had part of my education in French and spent time in French-speaking areas, my impression is that the -on suffix is archaic and nowadays gets used only in those -on nicknames, like Manon and Marion that have become full names in their own right. If I called my friend Sylvie Sylvion she'd probably wonder what I had been smoking.
-ette feels slightly less weird but I'd say none of the suffixes you mention would get added to names like -y or -ie in English, it's once again more the case of diminutives turning into full names.
As nicknames go, these days, people are more likely to shorten a name instead, eg using Véro for Veronique or Isa for Isabelle.
Formerly Known as Murasaki
This message was edited 7/8/2010, 6:54 AM