Hey Tuscan - I'm all for modifying bikes as you know (you should see all the others I have, especially the latest one x) - but there comes a point when you are, as they say, p!ssing in the wind!
As Regie points out above, the Tenere has been build as an overland bike, not a desert racer - it is designed to carry a passenger and a lot more luggage than an XR650 could ever hope to... It is designed to ride day in and day out with little or no maintenance, and long service intervals... it has a full fairing and huge fuel tank as standard. A large battery, a huge comfy seat, cat equipped exhausts, twin front disc brakes, large headlight... oh and electric start of course!... hell I'm boring myself here... but you get the picture.
An XR650 with all that lot on would be far closer to the Tenere's all-up weight. (I know this as I had an XR650R which I built up to a similar specification, including an electric start kit) - sure it was a good 20Kg lighter than the Ten' but you get what I'm saying?
Seriously, changing the swingarm - unless you really don't like the look of it, or just want an engineering challenge - is just a waste of time and money.
The point of the Tenere is it is a very comfortable and capable off-road touring bike - it will never be an edgy 'hard enduro' with a few concessionary comforts... if that is what you want, go for a DR/XR and mod it, or perhaps a KTM690 or BMX X-Challenge (although with a large front tank and fairing kit, those will weigh about the same as the Ten' does anyway), spend a lot of money, and you still won't have a bike that is as comfortable on the highway as it is in the dirt...
Seriously, when you have ridden your Tenere over the same sort of of terrain as I have (apologies for the trumpet-blowing, but do have a look at a few of the photo threads) and you are telling me that the stock bike is not capable 'enough' to ride that sort of terrain... well...
J xx