If it cost two fares to get from Ilford to Oxford Circus, the fact that the "Hopper" would work on the way back is academic, as you would have already hit the cap (equivalent to three fares).
For some, the smaller cost differential between the bus and the Tube will attract more people to the Central Line - which hardly seems to be a good idea, if my recent experience of it is anything to go by (had to let four trains go at St Pauls before I could even get to within touching distance of the trains)
However, if it really takes 24 minutes for a bus to travel the half mile from Centre Point to Oxford Circus, that's an average speed of 1.25 mph (Google Maps suggest it only takes 10 minutes to walk) so there seems little point in using, or indeed providing, a bus along there.
You could probably get from somewhere east of Stratford (although probably not all the way from Ilford) to Oxford Circus on one Hopper fare by using the 425 and 55, changing in Clapton.