Jeff,

Not sure what is meant exactly "by how far can this go" also this isn't a competition, i've found i've welcomed your questions to date.

The Predko example you cite was for demonstration purposes and if you read the text he failed in his intended purpose which was a simple serial terminal. Since you've implemented this project, you know that the displaying characters are from ROM. You also know that any peripheral service you might intend to include will have to "shoe-horn" into intervals which are now delay loops.

Everything is driven by the timing and the degree to which your target is "forgiving" of timing variation or irregularities.
I've been working from the point of view that video should be presentable across a variety of targets and to do this i've worked maintain determinancy and accuracy for the timing.

The major video breakthrough, from my point of view, was Craig's prodding to implement Video within an interrupt context, and then his interrupt entry scheme to achieve deterministic arrival to Video service routines.

This approach provided any non-video cycles to foreground or lower priority interrupt tasks. Using a fast executing micro you will find plenty of room for alternate tasks.

Now schedule and the time spent prototyping platform circuits hasn't left time to update my USER Video page, but implementing Page Mode 1 memory 8k or larger on a DS'420 i have code that achieves a glass TTY of 32 collumns x 24 rows of PC "VGA8" characters with supporting bit-mapped routines.

regards,
p