Will there ever be a firmware update for the 2018 Prime Plug-in?

Very unlikely

and if they do you will need a TSB and $$$

 

Does the phone charge if you take the case off?

 

All of the problems you mentioned are well know issues mainly with larger 11.6" HU on any year model of Prius Prime. Except for the frequent re-booting problem, firmware update even if it exists is not likely to solve the problems you mentioned. Bluetooth audio quality, I think, is inherent to the connection. The same sound source either by the BlueTooth or direct USB connection, the direct connection always sounds better. The album artwork of whatever is playing is almost never displayed on purpose. It is a safety "feature" Toyota implemented to only allow seeing the album artwork if you have your car in Park, never when the car is in motion. iPhone disconnecting from USB has been reported, but I don't think any firmware update has solved the problem. And Qi charger in PP is so weak as to it is totally inadequate for today's power-hungry smartphones. You are much better to just plug in high wattage USB-C PD car adapter. I use a 63W PD adapter, and my Pixel phone can be charged in less than 20min from almost 0% to full.

 

nupe

 

I have the small screen, and I guess I've never tested wired audio. I just went for a short drive to try it. Since my phone is android it didn't work with the USB connector.

I tried switching between an aux cable and bluetooth. The aux cable sounded a little better, but it was hard to tell for sure. Probably not better enough to notice while going over 45mph, and probably not enough to be worth the downsides. But I have the base audio system, so maybe it's more noticeable with the upgraded one.

I have one of those stupid phones without a headphone jack, so to make it as convenient as bluetooth I'd need a wireless charger to charge the phone while playing music, and a phone mount to let me switch tracks on the phone instead of the steering wheel buttons.

I'm thinking of adding a wireless charger anyway. The "phone cubby" is too slippery and too short. If I just set a wireless charger in it, it would level it out with the front of the cupholders, and hopefully it would have a grippy surface.

 

There have been several updates for the navigation receiver assembly (head unit), but I don’t know if they solve the specific problems you’ve mentioned. At this writing, the latest one is described in Toyota bulletin T-SB-0031-20, “Audio Head Unit Software Update (Denso)” (PDF), April 1, 2020.

If the car is still under warranty, a dealer could install the update at no charge; I recommend this option, since if the update were to fail, replacing the head unit would be costly. The files are also available with a Professional Diagnostic subscription to techinfo.toyota.com (from $65) and, perhaps, from the securedp.toyota.com website, which may or may not have the latest version.

As for the wireless charger, I don’t think anything has changed since my January 2019 posting.

 

Order another Anker charger pad, affix and wire it to your vehicle, and enjoy the result.

It's been proven many times over- automakers are not keeping up with the pace of smartphone product technology. Frankly I think it's embarrassing that they still try, rather than play nice hosts to standardized field-upgradable modules.

 

I just wish they would update their maps. Google maps on the phone are so much better.