ITP (v1) is already in the wild, and the next version can be previewed with Safari Tech Preview.
Luckily, as of now, you don't have a terrific amount to worry about with regard to Marketo's Munchkin analytics library. ITP is designed to thwart cross-site remarketing, not to prevent same-domain journey tracking. While some of its measures can impact 1st-party cookies like the Munchkin _mkto_trk, with proper preparation you should be OK.
Because of ITP, we no longer recommend embedding Marketo assets in third-party sites -- the prime example of such assets being Marketo forms -- using the same domain you use for Marketo Landing Pages. In other words, instead of referencing //pages.example.com in the form embed code, allocate a new Domain Alias in Marketo (and corresponding DNS registration + CNAME RR, of course) like assets.example2.info and load embedded assets from there instead. The intent of this setup is to prevent the same cookie from being seen in both 1st- and 3rd-party contexts.
But despite the optimistic take above, more research is necessary. And Apple doesn't make this research easy. Amorphous references to "machine learning" -- some say the learning corpus is built on the local machine only, but I don't buy that -- mean someone has to dig into the WebKit source code. Yet, AFAIK, no independent person has done a technical deep dive, despite WK being open source (though I'm not sure there aren't closed-source components at work here as well).