I have been using XnView for so long, the continuity of its identity (via the icon) is very well etablished for me. Perhaps it is the same for other long-time users.
I'm not opposed to change. To be quite frank, I initially downloaded and tried XnView because of the attractiveness of its "little art works".. that is, the original logo and the original toolbar icons (the orange-themed ones, if you remember). The Mezich look (which I like and approve of) now dominates.
The Altap Salamander team went though this process a few years ago. They contemplated changing the name AND the icon, though fortunately they only changed the icon. From reading the forum over there, I could sense how difficult a design/decision it was.
A thing to keep in mind also is that some people care, some people notice but don't care, and some people don't even notice. I'm probably in the "care too much" group.
Here are some icons from my desktop toolbar.

IMO, the existing XnView icon is the least easy to recognize (as a control), though of course now that is the feature I use to identify it... XnView is the faded little thing that is "barely" there.
There are several dimensions of icon design... aesthetics, recognizability (as to product), recognizability (as to control placement and activation), uniqueness of form (so as to distinguish it from others), confusion factor (what is it?). If we made a scale for evaluating various proposals, I'd personally would score things (1-5 for positives, -5 to -1 for negatives) like this:
Current XnView icon
Aesthetics: 4 (nice looking)
Recognize as product: 4 (yup, that's XnView)
Recognize as control: 2 ("hard to see")
Uniqueness of form: 3 (vaguely similar to some other icons)
Confusion factor (negative): -1 (a little confusion, but not much: looks like an eye, but also a splash)
Score 14
Thibaud's latest version
Aesthetics: 4 (nice looking)
Recognize as product: 1 (no history yet, little visual connection to current product)
Recognize as control: 5 (easy to see and distinguish)
Uniqueness of form: 3 (vaguely similar to some other icons)
Confusion factor (negative): -5 (could be an bear paw, could be lips and tongue)
Score 8
Is this approach useful to the current topic?