Mmh, how does that even look? Anything like the ones used in the "Oceans Eleven" movies? I've never bothered to watch the series and YouTube isn't particularly helpful this morning.... I would assume, though, that it's not done in a compositing program. No doubt it's a matter of production time and cost and it's easy enough to do with some simple linear and block wipes in a multi-track editing program...
I can't remember what the Ocean Eleven opening looked like--- Here a very simple example of what I was talking about.
Keeping the boarders a consistant size was much easier in AE as the boarders are solid layers that can be duplicated, moved/scaled, and faded as needed. I guess I could have also tried making the boarders out of a single Shape layer with animations of the shape within it. There are probably expressions that could make this quicker to do.
The crop feature in Pr is nice but didn't offer the flexibility of animating masks. With Mask I could have gone further than straight Verical and Horizontal lines.
I guess, maybe the way to approach this is to first do the cell changes with Masked Solid Layers and then replace with the Solid with footage and last to add the boarders. You also use the Write on effect to create the boards.
As someone with a lot more experience than me, I would like to know how would you suggest a project of this kind be approached.
If you need a wipe with borders, then some commercial plug-ins have this feature. In AE, indeed I'd probably rig it with expressions, so the gaps stay at a consistent width when changing the crop areas and placement. It's not that difficult to set up, but I never have thought that there could be some demand for such stuff, so I don't have project handy. Maybe one of those days.... For the time being you probably can get quite a bit by using the Silhouette Alpha blending mode and creating the frames at the top of the layer. You could then move and animate items independently below and crop them further with masks, wipes or mattes. Also consider moving stuff with Motion Tile or the Transform effect rather than their native transform properties based on pre-comps. That makes it easier to retain a consistent appearance...