A friend and I were seriously looking at building an SAC rig recently. It may still be on the table but reading the official and non-official forums gave me a bad feeling about it. I am sure it works but it is NOT flexible as far as user interface. No new features or configuration options for the last several years. And it is not keeping up with modern OS. I think SAC was WAY ahead of it's time. But the attitude of the creator/programmer is a little to hostile if you need it to work some thing other than HIS way.
For me SAC works great. Not sure what you mean by not flexible. I've thought about moving back to a physical board but I can't find one under $10k that will do everything I need. I like that I can rearrange channels and setup custom views. I like being able to use VST plugins (most of them are free). I like having 24 ins and outs or more if I need. I like being able to control the whole system on my Windows 8 tablet or my laptop or my FOH rig with a 23" monitor/keyboard/mouse. SAC isn't for everyone and it's not the answer for every gig but it has it's place and I find it very useful. I do miss having real faders but it's a compromise for all the other features. And as far as new and improved versions go... yes I have a wish list too but just like any other console, if it does what you need great, if not then there are other options out there.
On a side note... I wish someone else would step up and put something else out like SAC. How hard would it be for something like Reaper to be tweaked exclusively for live use? But that's another topic in itself.