Nick, this is hard to guess. One may want to have a look at what brands make knives where the prices exploded. It seems to come with either knives being visually appealing (Shigefusa, Ashi honyaki, Konosuke) or with a grind that was atypical (Kato / Workhorse).
In the last few years several custom makers have reached a rather high status like Rader, Andy Billipp, Haburn and more are rising. However their prices for the higher end pieces are already well above $1000 so while they may gently appreciate over time, I do not see overly large potential there.
In general I do not expect that apart of stuff like Yo kitaeji to get past $3000 as simply the number of people that are willing to pay that much is still limited. In other words - ‘proper’ art collectors did not discover kitchen knives yet. And once they will, they will go after custom knives, not those made in Japan that are made by undisclosed craftsmen.
Just an opinion of someone who knows awfully little about the ... special .... mind of collectors.