History Masking and Timeline

Question

Disclaimer: this feature request doesn't fall under the "absolutely essential" category, and at this point it's only a rough idea.
I'd like to have a timeline with sliders (like in a movie or animation program, but actually more like when creating Photoshop gradients, as I'll explain). The timeline would default to one slider at the end of the timeline, indicating that all vector elements are visible. Sliding this slider backward would gradually hide elements, beginning wtih the most recently created. As when creating a gradient, new sliders could be created to only mask elements created earliest, or sometime in the middle. "Keyframe" markers could easily be added at any point to mark the beginning and end of work periods so that they can be easily masked.
Perhaps the most useful function of this tool is that it provides a quick way to unclutter a document. Working on an elaborate illustration? Mask the first half of your work so you don't keep accidentally selecting it (or mask any other point in your history where you created invasive details). When you're quickly sketching, it can actually be most intuitive to "bound" regions by time rather than space -- simply highlight a rough period of your history that you want to make dissapear for a moment.
But, the tool would provide many creative oppurtunities. First, this would be an easy way to fiddle with illustration states, rather than saving copies, hiding and unhiding layers, etc. -- especially when you're trying to quickly sketch an idea (and, say, want to play around with shading styles). But this would also be a creative tool, like Photoshop's history brush, though this interface would enhance that concept significantly. Sliders are an intuitive/natural way to navigate history. In some cases you may not know precisely what "frame" you want to return to, in which case casually fiddling with a slider will produce the best results. And, just as many professional artists begin with scribbles, which gradually take form, playing with an objects timeline (masking random portions) could simply serve as a fun creative tool. It would be interesting to see, for example, what it looks like when you partially obscure a period of your line art history and a period of your color history -- the effect would be unique on your order of operations, how you color, etc.
Thoughts?

Answer 1

Good suggestions Wim. Both are much requested items, but it is always good to revisit them!
The masking debate is interesting, as it can be combined to localize all edits. Mark Hamburg (adobe) participated in one thread on how this might be accomplished. As I recall, there were two schools of thought (at least): selection vs painting. It was quite exciting to see Mark participate and illuminating too - in the depth of thought that goes into these "features".
Adding the perspctive control to the crop is a logical extension a la photoshop. I hope this is just a matter of time, as the Lr team works their way down the priotity list.
Cheers
Rory