One of the primary reasons I went with this website software was due to it's support of so-called 'responsive design websites'.
Being 2013, we've now had modern smartphones (I differentiate these between what was called a smartphone pre-iphone introduction - clunky interface, and most importantly, terrible web interface). Various reports announce that 45% or so of all searches are completed from a mobile device but even taking away from the stats, even common sense should dictate nowadays a website that can support smaller screen devices. Maybe I'm wrong? Even looking around, it's a lot more common to see a smartphone (be in Apple, Android, Windows) than an older 'brick' phone.
I've been involved in a couple of website re-designs in the past couple of years, some of whom ensured there was either a specific mobile-formatted website, or else one that was 'responsive' (an excellent slideshow explaining exactly this topic). I've also been involved in a few sites (my old employer) that were only created newly in the past six months that still have no support for smaller screen sizes - a wish I expressly pushed for without success. While it's something that you can probably still (just!) get away with, as more and more people move to the use of tablets, etc with smaller screens (most no larger that 9 or so inches), illegible text and links will become more and more of a turn-off for visitors to your site. Taking a recent example with Flash content on websites - fully capable versions to replace the content which would not show up on iOS devices is widespread.
So let's define 'future friendly'. Personally I see it as supporting the majority, but also trends and technologies that are on the up and coming. We are not taking about elite, 1%, items, but more things that have a noticeable impact across a majority of users. Mobile devices now make up such a large part of the sales market for computers, it's inexcusable to ignore them.
Is your website 'future friendly'?