Jim,
I also wanted to say 'thank you' ... for initiating this discussion. I've been wondering the same thing about how things worked and some 'best practices' ... which is coming out of this thread, I think.
I'm also in agreement (with you) that you'd probably want to reserve am entire 512ch block for DMX, like your thinking.
I never thought a few years ago I would have been up to 256 LOR channels already. I'm adding (7) LE's this year, so another 112 channels of DMX. If I eventually convert my LOR controllers to LE, which is likely., then I'd be using 368 channels of DMX already in my 4th year. So I think its certainly possible to need 512. I"m also going to have a bunch of pixelnet channels as well, for the SS items.
I've also wondered about DMX channels for regular (non LE) DMX controllers (like the $8 3CH DMX controllers dmoore uses) ... and how to assign those DMX channels (or rather, where to start numbering them). So for me, I've got another 24 channels of that kind of DMX (non-LE dmx controlled DMX channels) .... and was wondering if I would start at 512 and maybe work backwords ... in terms of assigning them. So like 488->512 would be for standalone DMX channels, and I'd use 1->368 for the LE DMX channels ... having the room to grow either way.
I have two dongles, and was thinking of using one for DMX (512) and one for pixelnet. If I use both, then I was wondering if I could use channels DMX-Dongle#1 DMX 1->512 for LE controlled DMX channels, and then use PixelNet Dongle#2 with 1->256 (or some number between 100 and 512) for regular DMX channels (reserve that range), and then pixelnet on the balance of the 4096 pixelnet channels.