There would be many more possibilities for new and reinstated old routes ex BHX with the runway extension in place.
Airlines such as AA struggled with payload restrictions with 767-300 equipment
Certainly ORD,ATL,JFK, (Delta Airlines supported BHX plan to lengthen the runway)BOS,IAD,IAH,MIA,LAX,SFO,DOH,DEL,BOM,DAC,SIN,BKK,HKG,P VG would all be possible and possibly more profitable with the runway extension in place.
As for holiday makers certainly more SFB with the A330s of TCX and MON which currently cannot use BHX runway outbound non-stop. Mexico, Caribbean and Indian Ocean MLE,CMB,MBA would be do-able without a stop. YVR, DEN and YYC for Winter ski charters would also be possible.
Note this isn't a wish list just a list of routes that would be possible (some or most of these may never operate ex BHX) but are possibilities.
One of the above routes may well be announced in the near future watch this space!
Daza