473: Wooler to Alnmouth Station (extend the 473 to Alnmouth Station to open new rail links and connect with trains)
X73: Kelso to Almouth Station (runs direct from Powburn to Wooler and extends to Kelso)

The 473 would be as now but extended to Alnmouth Station, the X73 would run once a day and connect with a key train to get into Newcastle for 8.30'ish and a train leaving at roughly 5.30pm so everyone has the bus which connects with the train. 08:00 at Alnmouth and 18:10 from Alnmouth seems the ideal time as there's a XC train heading to/from Newcastle and a LNER train heading to/from Edinburgh at these times. 

X16: Withdrawn, replaced by 473/X73, why duplicate services and the X73 would be quicker anyway, excluding Morpeth.

If advertised well, and appropiate fares, I could see that X73 being popular. Heading home from Newcastle, someone leaving work at 5pm would get home to Alnwick at 6:30pm'ish rather than 7.20pm it's substationally quicker than the X15.