Choosing a new audio interface

Yes, you can. I connect my two digital piano as follows:

Kawai CL35 (MIDI DIN5 output) -> plug to plug DIN5 cable -> Berhinger UMC204HD (MIDI DIN5 input) -> A to B USB cable -> PC
Kawai MP11 (MIDI DIN5 output) -> plug to plug DIN5 cable -> Berhinger UMC404HD (MIDI DIN5 input) -> A to B USB cable ->PC

Pros:
Requires only one USB port (Convenient for minimizing laptop USB usage).
Cons:
You'll need a plug-to-plug DIN5 cable (two if you want to enable bidirectional communication).
Not every modern digital piano has DIN5 MIDI jacks.

In my case, I prefer this setup because it allows me to communicate my laptop and the digital piano with just a single connection. This is particularly important for me since my laptop has only three USB ports: one for the mouse, one for the piano, and the last one in reserve.

I don’t think Motu has a model with the outputs I need.

Very interesting. My Kawai NV10S has both USB to host and MIDI in/out jacks. I am using the MIDI in and out with a Roland UM-ONE with a USB plug to my PC (a Lenova Tiny P360 which has plenty of USB slots so not a problem there).

The part that intrigues me is the possibiity of doing away with the analog output I'm feeding from my Focusrite 2i4 back to the analog line in on the NV10S. I do this so I can mix the sound going to my Yamaha HS7 external monitors and the internal sound system on the piano. There are some weird artifacts (occassional loud 'popping' noise) through the DP speakers which appear to be related to the analog line-in volume adjustment on the Kawai and I like the thought of a digital input back into the piano instead of the analog line in. My understanding is that USB-to-host is one way (I also have a Yamaha P515 with an internal audio interface where the USB goes both out to the PC and back into the piano). I'm curious what the MIDI in on the Kawai does and if it actually allows a digital signal to be processed by the piano if I go MIDI in + out directly to my Focusrite. All my wiring's tucked away and before I start tearing it apart I'll try to confirm that what you're describing will work on my piano so that I can eliminate the analog line-in.

A Motu M4 ?

I have some old keyboards which the company no longer supports with drivers. Audio interfaces with midi i/o tend to be better with updating drivers, in my experience, so it's ok to go midi from keyboard into the interface and let the interface piggyback the signal over usb. But it is better to use usb from the keyboard to the computer if a proper driver is provided because it will provide better functionality than the generic midi some interfaces provide.

I have a MOTU M2, the updated model from 2021. It's pretty good and it was a good buy. It has been reliable. It works on Linux by the way. The M4 is like the M2. It has more ins and outs. You can connect the keyboard to the midi of the MOTU if you prefer, but I use the USB and it also works fine. It can sample fast. I run it up at 96k which gives a small improvement over the default.
The M2 has balanced jack, RCA, and headphone outputs with volume controls, so it's a DAC-preamp. I actually use the headphone output connected to an integrated amplifier. The balanced output is more powerful, clean and clear, but I find it a bit harsh. The headphone output sounds more pleasing. The RCA output has less volume. The specs in the manual are balanced TRS 16dBu, RCA 9.5dBu, & TRS stereo headphones 12.5dBu.
The input preamps are pretty good.
I'm thinking of buying an audiophile DAC as an upgrade for using with Pianoteq and the computer. But then again maybe not. It has been synergising pretty well recently.

For the balanced TRS to RCA you ought to not connect the cold wire (according to the manual). This cable is non-standard, so not easy to buy. You can make one up yourself, or get two TRS stereo <-> 2 RCA cables and just use one of each of the RCAs, the one which has the stronger signal. To use the headphone output, which is what I do, you need a TRS stereo <--> 2 RCA cable.