If files are always organised by date then any programme and any OS can deal with and maintain your file structure. Essential for anyone who intends living at least another 5 years! New software will appear, old software will disappear. That is ineveitable, you just won't know what will survive.
So if you add keywords to images as well and keep them with the files and not just in LR's or Aperture's database, then any other decent software should be able to read the keyword metadata. Besides it's quite easy to export LR's Keywords as it's just a text file. Again any decent software should be able to import something that basic to maintain any keywording heirachies you've made.
The major and oft ignored problem with relying on keywords to find stuff is that it takes an awful lot of effort to meaningfully keyword one's images, whereas importing by date and labelling folders as well is very easy indeed. LR and Bridge can easily do that for you and that's the important bit, being easy as then you'll actually do it.
Keywording in LR is a big step up on before, but it's still a lot of effort and time consuming to do, so it won't always get done. Besides, if you repeatedly shoot the same subject, as most people do, words like landscape, tree or kids will simply bring up 1's of 1'''s of images which kind of defeats the purpose. Also if you tend to file by date, you tend to start remembering when things occurred better than before, so it gets easier with usage.
Date heirachy is content agnostic and expands logically. A content/descriptive heirachy is unwieldy and breaks down if you have items that can go in more than one folder. I used to use it and it's fine for small collections, but falls down too quickly.
Somethings can stay outside of date folders, Client jobs may be better served by a client heirachy and things like wedding shoots may be best done by couple's names as that's probably all you ever need to reference the work. Though any possible portfolio shots should be marked/labelled as you go along.