Since the code is available, as we discussed some years ago at a Chicago TI Faire, you could create an F38A as an upgrade for the F18A. I know the late great Gazoo and I have posed questions to you about an upgrade to the F18A. Tursi and I have also had conversations about adding a full implementation of the v9938 to Classic99 as well instead of the current partial implementation. Again, the emulation code is out there. I have little doubt that there will be 80-column devices produced in the future that take advantage of the capabilities of 9938/9958 based systems (Jim Fetzner is a possible source) since the schematics for the Dijit AVPC and other advanced cards are available and there seems to be an adequate supply of the chips from Chinese and other sources.
You could use TELCO as an example and have program modules for an application that use the enhanced VDP space (ex. 27 program modules can reside in VDP with a Dijit AVPC card.
Physically, how would such a device plug into the 99/4A? I'm still looking for an answer to the hard technical problem that is being avoided here. To connect a 9938 you need extra physical pins connected to the VDP that do not exist for the 9918A. It is not a "plug-in" solution. If it is done as an expansion of some sort (instead of replacing the 9918A in the console), then there is no software support.
Sadly the biggest use of the 9938 was the extra VRAM to supplement the system memory, and IMO the [S]AMS is a better memory expansion solution for the 99/4A. The second biggest use was the 80-columns, which the F18A can do. I have yet to see any 99/4A software that uses the graphical enhancements that the 9938 provides, especially when compared to a system that did use the 9938's features like the MSX2.
If anyone can come up with a way to provide a 9938-style VDP to the 99/4A in a way that non-hardware-hacker users can install and use, I am open to hearing the technical details on exactly how it can be done. I'm not really interested in vague discussions or hand waving. Show me something seriously technically viable, and I will seriously consider it.