I have the following proposal for a future facelift of UFX III

From highest to lowest priority:

1. Using SFP modules for MADI would give a few benefits to customers and RME
— customer can switch between single and multimode fiber as needed, no need for special orders anymore
— if a transceiver should become faulty, you can replace it easily (hot swappable), no repair cost
— more unique cabling (LC/LC) between newer RME devices, instead of a mix of SC/LC and LC/LC cables)
— SFPs are compact, would maybe even allow for a 2nd MADI bus

2. 2nd MADI bus
When using M-32 Pro AD/DA converter at double speed, then one MADI bus is quickly full and doesn't allow connecting other devices like preamps or format converter. Also (see point #1), using two SFP slots would much likely well at the back of the unit. Additionally, two MADI buses would more easily allow for setups to work (at double or) even at quad speed if somebody should get such a project or demand.

Currently, UFX III with M-32 AD and DA and 12Mic is only possible at single speed if you want to operate all devices together. Otherwise, you would have to change the MADI channel assignment (routing) at each of the MADI devices depending on sample rate, which creates operational overhead and is harder to handle.

3. Instead of 1x AES I/O I would propose 4x AES I/O with DB-25 connector like the Octamic XTC has. This would enable for additional use cases without having to spend money for an additional format converter (to be connected via either ADAT or MADI). Use cases: external FX, devices like Axe FX, applications like 5.1, 7.1, maybe even connecting multiple ADI-2 FS or ADI-2 Pro FS R BE or ADI-2/4 Pro SE.

IMHO also, beneficial for the concept of the UFX II which has no MADI and could much quicker become full.
You could connect external FX or devices like AXE FX via AES and would have more analog ports free for other purposes and would save AD/DA conversion in the FX units. 4x AES I/O should still fit for USB2.

4. PSU redundancy
2nd PSU like in newer products like M-32, M-1610 Pro and 12Mic. When using a HDSPe MADI FX then you would have the 2nd PSU in the Workstation or Server (Desktop/Rack device). But when using UFX III flagship device or Madiface XT, then power redundancy is missing. If there is no room or if the price should not become too expensive, maybe implementation like in 12Mic, not 100% sure whether this makes sense only for a preamp.

Base price higher, but still benefits / savings in certain situations

OK, the price would be [a little ] higher, but depends on whether only a few or all things would/could be implemented.
At least, you would have significantly more options.
Furthermore, it would save you the money for additional format converters if you need more AES ports.

What are the alternatives?

Getting HDSPe MADI [FX] or MADIface XT is not an alternative for everybody. Those devices are nice and powerful, but are missing some cool features, that the flagship devices have. Furthermore, the flexibility to be connected via USB.

More in particular:
XT: has no instr inputs and older preamps with less preamp gain and is missing DURec, Room EQ, Crossfeed
HDSPe MADI FX: has no analog ports at all except unbalanced for phones and is missing DURec, Room EQ, Crossfeed

What do you think about that?