It seems like the southern Interstate 87 is coming into play in North Carolina and Virginia (later). This means there will be duplicate Interstate 87s. Unless I am for some reason mistaken, this will be the first north-south duplicated interstate number.
I've talked about this in the Southeast sub-forum, but I honestly think the southern I-87 designation would work far better as an Interstate 46. Interstate 87 isn't really breaking any rules in the grid or anything, I just personally think it isn't the best number for the interstate, as avoiding the number 87 would avoid having yet another duplication of a number, and the corridor is a little more east-west than it is north-south anyhow.
With that said, it sounds like we will have to accept the Interstate 87 numbering, and with that said, I would be all for extending this new I-87 corridor north onto the Delmarva Peninsula, up to Wilmington, Delaware, then possibly have a brief concurrency with I-95 then I-295 into New Jersey, then have I-87 routed along the New Jersey Turnpike and later concurrent with I-95 along it until reaching New York City, and reaching the current, northern Interstate 87. Should that happen, the southernmost section of current I-87 from I-95 to I-278 could be an unused even I-x87 interstate designation, such like that of how I-75 in downtown Knoxville, Tennessee became Interstate 275. That might potentially sound wacky - possibly either like a really good idea or a really bad idea. But it would connect the two I-87s. While a lot of I-87 would be out of the grid, its southernmost part in North Carolina between Raleigh and I-95, and all of the current, northern I-87 in New York would not be. This could also work since it looks like they aren't going to change the numbering of I-97 and I-99 (which are both badly numbered, but that we have all long accepted, besides our fantasizing), and should a proposed Interstate 101 still come into play, it could connect I-87 in NC to I-95 in GA or SC, serving the east coast in that region. That is the best way (that I know of) we could modify the creation of this southern, duplicate Interstate 87.