I was wondering if it's possible to see the status of an in progress file copy on the dock?

When you copy a file to a folder on the regular Win7 taskbar, there is an indicator that shows the file copy progress. Usually the folder icon fills up with a green bar as the file is being copied.

Is there an equivalent in the Nexus Ultimate dock?

No, there isn't something like that, to my knowledge.

However, and this goes to all the eye-candy requests, you have to understand that all that increases the CPU load. The normal Windows taskbar is able to do it, because it's part of the Windows Explorer, so it's the same process and the load is minimal. For an external application to achieve the same effect, it would either have to use its own copying routine or tap into Explorer's own data (*if* that data is even exposed) and continuously poll.
I know that nowadays CPU power is in abundance, but still, I don't want my CPU cycles wasted on useless eye-candy (and please don't tell me it's not).

Hooks like that don't use up more than a quarter of a percent of the available cores in the CPU, and the status animations are handled by WPF.
You really shouldn't make these kinds of excuses, it promotes a lack of ambition in the PC app community...

If Winstep released a plugin SDK for the dock, I'd do it myself!

First things first: I'm not the programmer of Winstep. Therefore, it's not my decision and what I say has no effect on any "PC app community" or whatever else you may have dreamt of.

However, it's not the "hook" that will cause CPU load, but the effect itself and, as you well know, the CPU load is cumulative. Any icon animation will add a lot more than "a quarter of a percent of the available cores" or whatever you dream it is. Try adding an animated icon in the dock and see for yourself.
I think Windows has enough CPU hogs just for "eye candy" as it is. The last thing we need is to add to it.

Finally, as far as I know, there are no plans to open up the plug-in infrastructure to the public. Jorge is very aware that it could attract some developers, but he's a lot more worried about the stability of Winstep and actually *losing* customers from badly written plug-ins.

Cheers!