I think upgrading US-70 into I-42 from the US-17 interchange down to Garner Road is do-able. It's not going to be the smoothest, easiest project. The main lane traffic will have to be shunted over to frontage roads and vice versa for bridges and slip ramps to be built. Nevertheless there is enough ROW there already for an urban-style freeway.
Farther South, between Garner Road and the turn for MCAS Cherry Point, I would expect the same design to be used: continuous frontage roads with an urban style freeway in the middle. There is enough space for it, except for maybe one or two properties partially in the path of future frontage roads (Riverside Camping Center is one example).
They can get away with the same treatment to US-70 going part of the way into Havelock. South of the intersection with Fontana Blvd/NC-101 the situation just gets a whole lot more difficult. No more existing frontage roads holding back property from hugging close to the main lanes.