I doubt this will be another Ark/WWE situation. The way they are presenting it, particularly in openly showing direct feed Switch screens and footage from the get go, suggests they are proud of their work. Plus, given CDPR's reputation, I doubt they'd want their 250-GOTY-awards-winning game to be tainted by association with an awful port job.
Given their reputation, how much money they've made on TW3 and pretty big user base on Switch, I would've expected them to go an extra mile and make custom port with fine-tuned art that will enable for better visuals and not this run of the mill downport.
There's nothing run-of-the-mill about getting a demanding open world game built to PS4 spec up and running on the Switch. This is a huge undertaking, by far the most ambitious conversion to the Switch to date. Yeah, building it all again with custom art would've been cool, but also crazy expensive, perhaps so much so as to not be financially viable.