Live blur

Question

So is there any way to get a live blur effect without using duplicate smart objects and masking and linking the layers?
It feels like we should be able to apply a gaussian blur to an adjustment layer which just blurs whatever is underneath it, and we can then just mask that. It's 2015, after all.

Answer 1

CPUs and GPUs are getting a little bit faster (GPUs moreso), but that still does not address the geometrically increasing requirements that a "filter layer" concept would need.
We tried this approach (and were met with a lot of expletives from prerelease users), and other apps have tried it -- but it breaks down very quickly with moderate (screen) sized images, and fails completely with professional (print, DSLR) sized images.
With adjustment layers, one pixel of output only requires one pixel of input -- that way the complexity grows linearly with the size of the adjustment/layer stack.
The problem is that for a filter layer to calculate one pixel of output, you may need to recalculate every pixel of the input (i.e.: large blurs, or distorts).  This means that the complexity grows geometrically (N^2 to N^4, possibly worse) with the number of filters and layers.  Just painting below the filter, or moving a layer below the filter becomes painfully slow - or you have to turn off the filters while you work below them (yeah, we tried that, too).
Smart Filters supply the same basic functionality, without the horrible performance penalty -- because the user makes an explicit choice of when to update the filters (by updating the smart object).