Question edited to meet new guidelines
I consider Netscape or IE5.5 to be irrelevant for the following reasons:
- Market share is negligible
- Mindshare is minimal - few developers still talk about the IE5.5 or Netscape problem and most web frameworks don't bother to support them.
- They are not official supported any more, unlike Internet Explorer which is still supported by Microsoft.
How long do you believe it will be before these conditions are met?
In terms of supporting your answer, you may want to consider Microsoft announcements, the timeline for depreciating other Microsoft products and current rate at which IE6 market share has been declining. You may also want to discuss in relative terms, for example, how much you believe that market share will drop off a year after Microsoft stop support.