I'm probably not the most qualified to answer this but Kindle Fire HDX 7" is 3rd generation, 2013, whereas the latest 4th generation HDX model (2014) only comes in 8.9" - no 7" version.
I saw elsewhere where someone asked if there was going to be a 4th gen 7" - but who knows.

(It's a little confusing to me, as Wikipedia refers to 3rd gen as 1st gen, and 4th gen as 2nd)

Anyway, having said that, what do you mean by obsolete ? What are your concerns.

The 3rd gen HDXs are updatable so far to OS version 4.5.3, just like the 4th gens, so at least they can keep current as far as that's concerned.

See Kindle Fire HDX Software Updates

Unfortunately, everything in the world of computers eventually becomes obsolete, it's just a matter of time. On the other hand, with the Kindle I'd imagine that typical functionality would be workable for quite a while. It's just that processors get faster, displays get higher resolutions, better cameras, and so on. But I'd wait for more input from people more familiar with the Kindle than I.

My 2nd generation kindle fire is still going strong. I also have a 2013 HD fire that still works great. If you take care of them they will last. Mary

The other thing to remember is that there will undoubtedly be updates to your Kindle Fire's software, but it will be more like gradual and subtle improvements rather than something that is a radical, one-step change.

Thanks to all for your input. All I want is a new Kindle reader with the capability of being taken on vacation to keep up with my email and possibly surf the net for interesting attractions nearby as I travel. My original Kindle reader is still going strong but it would be great to have a Kindle reader that also functions on vacation for email and occasional net browsing. Oh, I am addicted to ordinary, old fashioned Solitaire and would love to be able to play while I am stuck waiting for an appointment. Thus, I want a simple, reliable tablet and want to continue reading on the kindle format.

I think you're probably ok with the Kindle Fire HDX 7 then. It's highly unlikely that anything would come up that would make that reader unusable. If anything it would be hardware malfunction, equally unlikely, but that's different than obsolescence. Since it's new, it's going to have hardware stability and reliability just like any new gizmo, so I shouldn't even write that.
But as kudzu writes, his/her XP tablet still works.

(Of course, as soon as I write this they'll come out with a new Kindle that includes a digital hot-tub or backscratcher, so you always have to be prepared for a little buyer's remorse)

But go ahead and get the thing, and can you send us all photos from your vacation spot ?

Maine----The way life should be!

I bought a Kindle Fire (the original) for my wife many years ago. She really likes it and has read many books on it. She also plays games on it, still running strong.

I purchased myself an Acer Iconia a500 10.1" Tablet (w/ Android 3.1 upgraded to 4.0). I like the Acer much better than I like her Kindle. I have only read 3 books in the last 30 years, all of which were on my Acer. My Acer a500 Android Tablet is also still going strong.

I liked my Acer so much I recently purchased an new Acer Iconia W4-820. The New Tablet is only 8" and it's running Windows 8.1. It is an Awesome little Tablet, just like a Mini Computer. It has an Intel 1.8GHz Atom Processer and is pretty snappy. I can still read all of my books on this Tablet thru Google Play!

As for the Technology, as stated before there is always Buyers Remorse. As soon as you buy it you're almost guaranteed something new will be released. Just bite the bullet and buy what you want. I would suggest looking around at other brands and operating systems also. You just never know, you might like another Tablet better?