I love and use Superior Drummer on everything. They do some updates from time to time but for the most part they leave the basic product alone. New libraries come out. and they have been 64-bit for years.
I find that I only use the Nashville kit because it is so good and so versatile.
For me SD is like an old friend that I can always rely on. I would not feel that way if they were still 32-bit....

mixmkr
another in Superior....well at least EZD...is the electronic kit.  I use it in Superior because I can then tune the kit and the other great Superior stuff.  But to audition a "drum"...you can't scroll...you have to click...the "choice window" then closes...etc, etc... VERY cumbersome...and with 75 kicks to chose from, I've just gravitated to my favs..  Never really had the desire to scroll thru them, in the fashion they have it set up now.  Need the ">" buttom somewhere for sure.  I also think the X drum feature could be made a lot easier, even though I finally got me head around it.  And yeah....I don't need 50 busses to route drums..
 
....oh and turn down the HH on ALL their kit presets!

Keep in mind that they have supported not only Windows but Apple formats as well as the work put into Win 64 support as well as RTAS, and AAX versions.
 
The library releases have been steady for EZdrummer, Superior Drummer 2 and EZmix.  EZkeys has come along as well so it's not like they are sitting on their hands, for sure.

For me; movable/re-arrangeable tracks & buses in the mixer section

Amen to that! It's great they provide so many busses, but who has ever used them all? Let me hide the unused ones.

 
This was a major thing for me that drew me to BFD2 (apart from the sound) over superior. BFD2 doesn't provide you with any buses unless (or until) you want them and then you can locate them anywhere you choose on the mixer. I always like to have mine adjacent to their respective kit piece rather than sliding back and forth across the mixer every time I want edit.
 

And while we're at it, how about remembering the last mixer view so it comes up that way automatically when I re-open a project?

 
I didn't know it couldn't do that ? That seems very odd that it doesn't.
 

Also on the wish list: an integrated distortion plugin, the ability to type in values into the effects plugins, global bleed mute and effects bypass buttons. 
 
Other than that, it's perfect.

For a lot of users, (perhaps even most) the included effects of any drum vst aren't an issue as they bus their tracks out to use either their sequencers, or other third party effects. BFD2 came with something like 30 effects that were very drum orientated including special editions of PSP's vintage warmer and Breverb. in 2007 these were top notch effects that were better than sonars and better than the majority of third party ones. Whilst there are a few advantages to bussing out to your host and using it's mixer and effects I found it so much quicker to use the ones in BFD2 and it just seemed to make more sense in a way. The only advantage I found in using effects in sonar was because automation was a little fiddly in BFD2 though I could automate any and every parameter that it had to offer.
 
With regards to updates, 64 bit and new kits aren't in my view, really product updates. There was a great review I read for BFD3 where the guy had praised fxpansion for not just sitting on their hands and knocking out new expansion kits every so often like other companies had been content to do but rather they were very brave and forward thinking in redesigning BFD3 from the ground up.
 
Still, if SD2 were to have all the new features that people seem to be suggesting here I guess they'd just have to make it more like BFD3
 
Steve