Hi - the answer to your question on whether or not a non-nexus device will get the latest and greatest android version when its released is..... maybe/unsure.
If having the latest version is a big draw for you, then you want to go with a Nexus device.
personally I was in the same situation - I bought an Asus TF300 transformer that came with 4.0 and that stopped getting updates at 4.2.1. Went with a Nexus the next go around.
Thanks for the reply Spyder. Good to see you around still. And that's pretty much what I figured.
So I went with the Xperia Z2 Tablet anyway.
The specs on the thing are just to nice for me to deny. It really is a beautiful specimen from a hardware perspective.
Waterproof, allows for memory cards (even if they are Sony's), thin as can be, powerful as all hell compared to other tablets, all of these things just made me kept coming back to it.
Finally I signed up for a Sony Credit Card awhile back now to earn the Sony Reward points, so as I hinted to earlier in the thread I had them, and more than I realized actually, so using them brought the cost of the Z2 down to below a Nexus 10 for me.
So I am going to own and really hopefully enjoy this Z2, then down the road if things really bother me with lack of updates, etc. I may look at the Nexus 9 and give this Z2 to my parents, as I have never been able to get them to use a computer no matter how much I try, but my mother is currently loving the Nexus 7 I got for them and really using it, her only complaint is sometimes things are hard to read.
So I might even have the Xperia Z2 Tablet by the end of the week depending on shipping. I will post some impressions once I do pick it up.
Thanks everyone for the feedback and opinions. It is much appreciated.