If a DE-1 superhighway concept were extended as a toll road to Salisbury from Milford on new location, it would likely be built on new location in Maryland as well, seamlessly tying into the Salisbury Bypass. Upgrading the rest south of there is mainly on limited-access roadway, and the connection to Virginia is debatable on what even happens in Virginia. If it's a new location in Virginia, then it would likely be new location for those 4 miles in Maryland as well.
Regardless of how well built US-13 is in Maryland, Delaware has always been the obstacle. Little if any of US-13 south of Dover would be useable for a freeway upgrade, probably all of it would need to be bypassed by a new location highway. Much the same for US-113 south of Milford.
Delaware's priorities for corridor preservation have been 1) DE-1 south of DAFB to beaches, 2) US-113 south of Milford, and 3) US-13 south of Dover. US-13 is at the bottom of the barrel. Also no cross-connection between US-113 and US-13.
Delaware hasn't yet coalesced on over whether to utilize US-13 or US-113 as its future main north-south corridor, and that obviously influences what Maryland can do to coordinate with what Delaware decides sometime in the future.
Obviously all of this talk for a full freeway build out is fictional, since the I-99 proposal a decade ago, it's not been discussed heavily. Delaware mentioned in the I-99 "study" they have considered constructing a parallel freeway to US 113 like they've done with US 13 in the 80s and 90s with the DE 1 superhighway. Since Delaware is interested more with US 113, and Maryland is more interested in US 13, IMHO the best option would be to build a seamless connection between the two. Basically, upgrade 6 miles of DE-1 south of Dover to freeway standards (no tolling), then at Milford, construct 42 miles of limited-access toll freeway from Milford to Salisbury, seamlessly tying into the Salisbury Bypass about half way between the US 50 eastern exit, and the US 13 northern exit, and upgrade the rest of existing US 13 down to Pocomoke City. If Virginia were to do a similar concept stretching down to the CBBT, it would likely involve an additional 66 miles of toll freeway paralleling existing US 13, tying into the existing limited-access US 13 north of the CBBT, then upgrading it to the CBBT. On the southside, Northampton Blvd is limited-access to Diamond Springs Road, and from there to I-64, that's where it gets messy.
This would involve upgrading about 35 miles of limited-access roadway, at-grade in a full freeway, about 108 miles of new location toll-freeway total, plus about 5 miles of non-limited-access upgrades in Norfolk / VA Beach (if this is even done). If you tolled at 15 cents per mile, that would be $16.20 one-way, plus $2 one-way for the 45 miles of DE-1 freeway, plus $14 one-way on the CBBT, that's $32.20 one-way for over 210 miles of freeway, bypassing the I-95 / Washington / Balitmore corridor completely.
Driving the corridor at an average of 65 MPH (the CCBT is 55 MPH, rural freeway segments in VA likely 70 MPH, freeway in Maryland & Delaware at 65 MPH), that would save about 40 minutes of the existing drive on US 13. If the state's chose to try reviving the tollway concept through VA, Maryland, and Delaware (from the failed attempts before), it could turn out to be a great investment.
Using high-balled estimates, for 108 miles of freeway at $50 million per mile, that's $5.4 billion, and for 35 miles of upgrades at $30 million per mile, $1 billion. So about $6.4 billion to create over 210 miles of freeway from Norfolk to I-95 in Wilmington, DE, which would be backed with tolling.