There's no problem making an accelerating meter. The "perfect time" version fills the meter according to a linear function. It could well be a non-linear function.
A simple method of presenting a horizontal gradient would work in the same way but would not present a really smooth gradient, given the timing constraints.
A truly smooth horizontal gradient would be presented by using images of the bar (one for background and one for foreground) and unveiling the foreground incrementally as the swing progresses.
The construction of the bar with ding line, precision areas, etc., is really just a matter of image selection.
I, too, found the timing to be relatively free of additional tasks. I ran a movie of a Flight Simulator flight and experienced no visible effects. Of course, there is going to be a limit. The processor cores have a finite amount of time.
I'll be playing with this, no question. Hell, I spent a few hundred hours writing my own flight physics, and that only included in-the-air time.
Thanks for your responses and suggestions.
Incidentally, the progress bar was totally worthless in IE. Those guys had the best browser back at 4.0 (when their only real competition was Netscape) and have apparently been working hard to eff everything up, since.