Two things, an RCA input? really, not a con, considering the size of the device, it would be twice the height to hold the RCA plugs, nothing that an adapter can't fix. Optical audio Outputs, well I doubt anyone is going to notice the sound quality of a online streaming audio service.
Now for the other people don't see the purpose of this device....
For those of you who have a real stereo system, one which has stereo or surround sound system, this is the perfect way to listen to online radio, podcasts, and for those who want music throughout your home.
Listening to your favorite radio station on iHeart, Simple Radio skill, SiriusXM, and other services and even better if you have multiple devices. it's great if you entertain.
It's cheaper to buy one Echo Input then to buy two Echo devices with a speaker, all of the other devices require to use two of them if you want true stereo sound.
Most of the cheaper Bluetooth speakers are mono, and even if you use a good Bluetooth speaker that is stereo, the separation between the left and right will be greatly reduced.
Using two of the same Echo devices will give you true stereo sound, while using Bluetooth speakers.
So if you want true stereo sound, then either hook a Echo Input to your stereo or surround sound system, or a good pair of computer speakers. or buy a pair of Echo Inputs for true stereo sound to a pair of Bluetooth speakers, like DOSS Soundbox XLs, normally these speakers can't be stereo paired via Bluetooth, however with the Alexa app, it should be able to do this. 64 watts of power never sounded so good, who need a over priced sub-woofer from amazon.