These units seem to be referred to as "modular", and Pioneer has only a few models. The DMH-C2550NEX and DMH-C550NEX are the older models, which are described briefly here: https://www.crutchfield.com/S-iJQRdI...r-stereos.html.
This is the latest Pioneer one that I want purely for Wireless CarPlay that isn't out yet (maybe it ships in June?): https://www.pioneerelectronics.com/P.../DMH-WC6600NEX It retails for $900, and has all the bells and whistles. I very much like having CarPlay for my iPhone. My older Subaru doesn't have that, so we just use Bluetooth for music/etc, which has the advantage of not having to take my phone out of my pocket all the time. Wireless CarPlay is the best of both worlds for me.
The installation manual is linked on the page, and suggests that the screen can be positioned pretty much anywhere, and isn't very deep, so if you want to fabricate your own mounting frame you can put it pretty much anywhere. For example, you could probably slide a piece of wood or 3D printed plastic into the top of the center console under the trim from the back, and mount the screen onto that, thus keeping the vents completely clear (although possibly blocking the windshield a bit), and use the old single DIN radio hole for something else, or put the main electronics unit there. I think it has a 12" cable, but you can also buy extensions, which would probably let you mount the electronics unit under the evaporator box. Another option could be to hang the screen from the edge of the passenger kneepad, assuming it wouldn't be in the way of your passenger.
I'm still trying to figure out what to do with the mic for the hands free support on my current head unit. I clipped it to the bottom of the binnacle, but the car's just too loud for people to hear me clearly. I might try running it up to the sun visor, or possibly getting a more directional microphone aimed right at my face. Not that I do many calls in the car, but when I do it's nice not to have to fumble for my phone.
Most head units with screens also support rear cameras, which are very nice to have. You can get the camera itself on Amazon for like $30, then run the wire through a pontoon (which is what I did), or through a hole you make in the bulkhead. If you use ignition-switched power (instead of reverse light power) you can switch to the camera at any time, which can be useful. I'm currently having a problem with my head unit (I think it's a bug in the software, not a hardware issue), where it won't display the camera when in rear view mode until 90 seconds after you go into reverse, but the camera activates instantly manually. I haven't found a good solution to that, but I'm going to replace the head unit so I'm not worrying about it too much. I seem to be the only one with this problem, so I don't think it's a general issue with Pioneer units, just with mine.
You'll also likely want to get a parking brake bypass so you can use all the features without having to add wiring to your parking brake light, like pair Bluetooth devices and change some specific options. They're only a few dollars. I also hooked ups large capacitor to the radio's power supply so that it will stay powered while the engine is cranking, since full-featured radios like this have a pretty long startup time (5-10 seconds), and I don't want it to have to start over again after the engine starts, especially since it's not that uncommon to have to try a couple times to get it to stay running (I mean, it's not THAT common, but common enough). A side effect is the radio stays on for a few seconds when you turn the car off until he capacitor has drained, but that doesn't bother me.
-- Joe