As you can see you've pricked a nerve here. 10 pages of answers for what is essentially a simple answer to your question. The answer for you will depend on you and your preferences only. I know players who switched to 5 or 6 string and now never use anything else (so I guess for them 4 became obsolete). I know players who play both 4 and 5 string, even 4, 5, and 6. I have owned 4 or 5 5-string basses over the past 10 years and ultimately found that for me, they didn't work well, mainly due to string spacing. I have been a 4-string exclusive player now for some years. So for me 5 string basses are not a tool that I use. Obsolete? - no, just not the right choice for me.
Irregardless of what anyone else on TB says, the answer will always be, "depends on what works for you". All comes down to your own personal preference. Who knows, maybe someday I'll find that I need a 5 for something, in which case I'll buy one and use it. I'm not holding my breath since I never feel that having 4 strings is holding me back, but your experience may vary.