I think it really depends on where one considers the "main line" of the NE Extension to end and turn into just exit ramps. (Ignoring that these days, main line US6 uses ALL the "ramps" there.) Prior to I-81's construction, the NE Extension was proposed to go north to the NY state line, and the exit ramps were considered to start at the big 180-degree curve even though all traffic was forced onto the "ramps". After PA decided to take the federal money? That I'm not so sure... but until the ramps over to I-81 were built, all traffic had to go down to the surface road (US6/11) so one could argue that the "main line" of the highway continued to that interchange.
If we decide to move the end of I-476, I strongly recommend *adding* an extra waypoint rather than moving the existing one. That waypoint already exists on US6 and US11. But I'd rather keep I-476 as is if we can find a good reason to do so.