ya...aren't the thinkpad x series great?....sure the older x60 and x61 have a time with recent games...but...x61 and x60 can run a whack of linux distros with little hassle...and I think it is the x60 which is considered suitably perfect for gnu/linux libre distros. If you are gonna spend the bucks anyway...shuck it out for the x230...that baby can run ....and ya it is a bit heavier...but not as heavy as the m780...which is a beast with the optical drive...but ...you can simply take it out and throw in a 2nd hard drive bay...more storage...more distros ....a pretty mean beast with guts...wheeee!
But ya...bt or wireless keyboard will do in a pinch with a simple tablet.
And ya ...I agree...with the amount of current support for past models...

I wouldn't buy a new one either ...with what you need and wish it for...and at the "middling" price point you are aiming....either go lower and aim at specific usages...or go higher...go all out...then you most certainly will get the device you really want and need and it'll be ahead of the "depreciatory curve" ....so to speak.

Otherwise ...buy the brand new "middling" and you'll prob. regret the money spent for the value of the product and feel let down with what it can do....and for how long it can do it for...