Of course, the latter of the Yt fiber laser type goes for several million and requires 3-phase 480 VAC (I'm sure customs would frown on it without special approvals and paperwork). 120 kW - 150 kW lasers have been test-fitted on aircraft and naval vessels for use as weapons (yup, deadly lazar beams).
That being said, the former with a tube and a single-phase 110 VAC PSU goes for < $1800 USD these days (this amount may still exceed the value that would be subject to customs and importing). If that could works anywhere near the rated power and not get tied up in customs duties, that could form the basis for quite a bit cheaper applications than products several layers downstream in the supply chain.
Granted Class 4 need a minimum of safety features (keyed interlock, emergency stop, lots of signage at all entrances to the room and eye & skin protection) if going the DIY route and a water-cooling loop, it seems entirely within the realm of possibility to make a pretty awesome 2+-axis CNC for engraving and cutting thinner materials.
I just purchased a 150W c02 laser from China. When you import a laser from China. The FDA starts to care. They require that the import lasers that have an associated FDA Accession number for the product. Basically saying the laser is safe and has proper safety etc.
Having a customs broker for your first transaction is worth it's weight gold.
In terms of importing these lasers from China and selling it in the US market? I think you're a couple years late on the market for that one ;) There quite a few players that do that now.