That said, I find it odd that they didn't just resign PA 283 as PA 300, which I believe is its internal number. 283 isn't directly continuous with I-283, so why keep the same number?
PA-283 is a fairly reasonable extension of I-283, though if the whole thing were an Interstate, I'd think it should have an odd first digit -- since it would then not be connected to interstate highways at both sides, but rather would become a Frankenspur from I-83 into Lancaster. It would just require some reconfiguration of the interchange with the PA Turnpike, changing existing exit numbers on the current I-283 segment, and adding exit numbers to the current PA-283 segment. Maybe PennDOT once anticipated the whole thing would be approved into the Interstate system.
My opinion (and I don't know how doable this is) -- eliminate the PA-283/I-283 interchange with the PA Turnpike and construct a new interchange between the PA Turnpike and Airport Connector. The current PA-283/I-283/PA Turnpike interchange configuration is horrible. This solution would both get rid of that mess, AND provide more direct access from the PA Turnpike to MDT airport.
Problem is, the current I-283/PA Turnpike interchange provides access from the Turnpike to PTC HQ, so I doubt the PTC would go for it.