The latest projected release date for Drupal 8 is sometime in the vicinity of September 2015. The further along the Drupal community gets with fixing bugs the more likely that estimate becomes a reality. It’s a pretty safe bet that we’ll have a Drupal 8 release this year.
Certainly it goes without saying that a great deal of Drupal 7 websites will be upgraded to the next version, some immediately, and some later on. But what about all those websites still using Drupal 6, and even some that are still using Drupal 5? The end of life date for Drupal 5 was back in January of 2011, and you can be confident that the “official” end of life for Drupal 6 support will correlate with the Drupal 8, even though there is an initiative to provide some form of long term support for the populate 6 version.
Double the Security Risk
The types of security problems that were plaguing websites during the time of Drupal 5 have largely been addressed with newer version of Drupal, but as time marches on and hackers continue to strive to exploit vulnerabilities, new issues arise and have to be dealt with.
By sticking with an outdated and unsupported version of Drupal you face a double dose of trouble because not only did you not receive security updates for problems that were solved even three to four years ago, but your website is also not being protected against newer exploits.
Missing Out on New Core Functionality
The way the world wide web is utilized and what people expect from websites continues to evolve each year. The open-source nature of Drupal and its amazing community of developers allows it to continue to adapt and support these paradigm shifts.
The newest versions of Drupal have made great strides to support web standards, usability and accessibility requirements, and make accessing or working with Drupal websites over mobile devices a much more pleasant experience. Drupal 5 is behind the curve on all of these aspects, a fact that is unfortunate for your website’s visitors.
No New Contributed Modules or Themes
The contributed module ecosystem is one of its greatest aspects of the Drupal community. People from all of the world create new or improve existing modules which can be used (all for free) to enhance the functionality of your website. Because Drupal 5 is so outdated, few if any developers are creating modules for that Drupal version.
New website services and techniques come out each year however, but by not using a modern version of Drupal your ability to take advantage of those best practices will be lessened. This also applies to the graphical design aspect of your website with respect to Drupal theme templates.
Diminishing Developer Familiarity with Legacy Systems
The longer you wait, it won’t get any easier to upgrade or modify your website to a newer version of Drupal. Consider this, if you wait an incredibly long time to upgrade (Drupal 5 support ended in January 2011) the pool of web programmers who are familiar with the intricacies of that version of Drupal will diminish, thereby increasing the complexity and/or cost of such work.
Drupal has evolved quite a bit in the last two major versions (Drupal 6 and 7) and the changes are even more significant with the pending Drupal 8 release. Upgrading between version of Drupal has never really been easy, but this current step will probably go down as being one of the most significant yet.