Since upgrades are rediculously expensive, I am among those without an RTG card of any kind. So I would have to vote on support for at least AGA in your apps.
[RANT]
On a side note, it seems silly to be lacking cheap hardware out there... After all, using a PLD to translate between the Amiga and whatever chip a board needs is a pretty easy thing. Zorro to PLD to SCSI chip... BAM! New SCSI controller. Zorro to PLD to networking chip... BAM! New 10/100 NIC. Hell, even the PCI boards can be made dirt cheap with a PLD and one of QuickLogic's chips.
The hardest part is writing the driver!
[/RANT]