My first choice: A fresh tooling of a 1/48 F-101 B/F Voodoo. The whole Voodoo family would be nice actually.
Some others for 48th that come to mind:
DeHavilland Vampire/Sea Vixen family (please, please, pleeeease!
)
Ilyushin IL-28 "Beagle"
MiG-23/27 variants
S-2F Tracker
SAAB Viggen (The Viggen is almost gone from the skies, please say the old Esci, now Airfix, kit won't be the last word in 1/48 representations of that beauty!
)
This last one is a real looooooong shot, but would look great on the shelf next their MiG-15: I'd reeeeeally love a 1/48 kit of the Lavochkin 15. It never saw service outside the Soviet Union and by some accounts was a better jet than the MiG-15. Unfortunately it was more complex and Lavochkin was falling out of favour with the Soviet Government at the time and was just about to be shut down.
Like I say, a long shot, but I'd love to see it.