Interesting Q. and one we may all want to know soon.

FWIW I suspect you can't render as 4K, but you should be able to extract a "Proxy" 1080 file which will Render normally. Apart from the huge amount of Data 4K uses, I guess you may have to Upgrade - it will be interesting to see what features we are promised in SMSv14 -
Have you checked if the Camcorder has suitable software? It may be that they can provide the necessary Up-Proxy when the files are rough-edited using their "free" software - or maybe a "deal" to include Vegas, to clinch the camcorder sale.

I suspect we may need to improve the PC capabilities to handle 4K, although for Editing purposes a "Proxy" should mean we can use what we know works OK.

...Good Luck....

Note to Sony Software:
Can we Render 4K in sections? - if I need to Edit again, only those "sections" that are changed need rendering. - sections will need to be maybe 2-minutes each and there would be a "Section Marker" embedded so I can overwrite a COPY, thereby keeping the Original Render, as well as the Newer version of the whole movie.

If I have a 10min movie with a spelling mistake, it's crazy to need to repeat the whole Render, esp. in 4K - Estimate about 4 hours minimum, on my PC.
+++ It's Odd isn't it, that when I write "here" the website contains a spell-checker . . . . but not in SMS. -