Works fine with the stock heatsink ootb, even with a mild overclock.

They even have smaller than ITX systems now, though not quite as small as a NUC: https://www.asrock.com/nettop/

I have one of these and it runs great.

I run a Ryzen 5 2600 in a Cooler Master 130 case with the stock cooler. I run it with stock settings and frequencies (XMP enabled). I do not encounter any thermal throttling in normal usage, including long gaming sessions. That said, the 2600 is a 65W chip while the 2700X is rated at 105W. Maybe I would run into more thermal constraints if I used the 105W part, but so far the 2600 has had plenty of performance to meet my needs of a semi-portable gaming/development machine.

So far no heat issues with the stock heat sink (2600).