One of the advantages of using a Skyview radio with a Skyview system is that the EFIS integrates with the radio; you can load frequencies and otherwise control the radio from the EFIS, for example by viewing an airport on the map and loading a frequency for it to the radio's standby.
This video provides a good overview of the integration.
However, to my knowledge, the EFIS will only ever integrate with a single SV radio this way. That is, I don't think you can go on the EFIS and use the integrated controls while selecting between COM1 and COM2. Pretty sure the EFIS will only ever know that
a radio is connected. With that in mind, while you
can use a second SV radio for COM2, it'll be really no better than any other radio.
The other question to consider is switching between the two radios. Most of the GA aircraft we fly have an audio panel to switch between the two radios, and this panel controls
two functions. The first is what radio you're listening to, the second is what radio you're transmitting on. If you use a full-up audio panel in your build, you'll get this same functionality.
Another option here is to use the Dynon Skyview intercom. This is
not a full-up audio panel, and thus does not have the same feature set - specifically, there's no provision for switching between radios at all. To use two radios with the SV intercom, you'll connect the audio outputs for both radios to inputs on the intercom, and to decide which one you want to hear, you'll simply use the volume controls on each radio. Don't want to hear COM2? Turn it down all the way.
This gets us one half of the audio-panel functionality; the other half is picking which radio you're transmitting on. With the Skyview intercom, you'll have to install a separate switch to pick which radio you're transmitting on.
For my plane, I'm only planning on having a single radio. The SV radio allows monitoring two frequencies at once, which takes care of my primary use case for two radios. For the other one - an in-flight failure - I intend to carry a handheld as a backup, probably with a connection to a mounted antenna. (vs the rubber ducky) If I do decide to add a second built-in radio, I'll probably stick with the Dynon intercom, since the second radio will primarily be a backup.