Hey! This is my first post on TalkBass!
Welcome to talkbass. I hope you enjoy your stay, and visit often. Wow, is
@40Hz the only one with manners? Eight pages in and only one person to welcomed the poor guy to TB, before we started bombarding him with the 4/5 string argument. That said, I'll jump right in also.
First off I'll say, I kind of think the whole number of strings a bass has is much fuss over nothing really. What ever works for you. Like most everythings in life, it's all a matter of preference.
The thought of one making the other obsolete? Myself, I don't think so. They're all tools. We all seem to find a way to get the job accomplished with the tools most comfortable to us. Whether it's more strings, effects that give extended range (octave pedals and such), drop tuning, what ever. Personally, I tend to subscribe to the attitude that it's more about what you can do with a tool, more than what a tool can do. A very close friend play 5's only and teases me about playing only fours. I tell him "I guess I'm just old school" His response? You can play "old school" on a on a five. Here's right. I could if that was my preference. So, if you feel four strings are limited, get a 5er. But
it has it's limits, so get a 6er. Wait, those have limits so get a.... you get the Idea.
I can't argue that a bass with more than four strings will get a wider range, but at last check, there are still only 12 notes, and all 12 are found on anything from a Kala bass uke, to a 5/6 string bass. So, all and all OP, I personally don't feel a four string will become obsolete. If you're feeling the need for more strings, by all means go for it. Heck, there's a couple guy's out there that feel all you need is two strings. Bottom line......whatever works for you.