You've just created 9 or 10 slot pairs.
But, without wishing to restart the whole LHR expansion debate again, this is just stop-gap stuff. Over the next 20 years or so, there will be a substantial increase in the number of economically important destinations in Asia, LatAm and Africa which will require direct service to/from LHR if London / UK is to remain a pre-eminent business and tourist destination, and successive governments have just continued to dodge the issue. Already it seems certain that LHR will not have the capacity compete in the connecting traffic market - even if it wanted to - but at the very least it needs to provide unfettered access for those wishing to come to London as final destination.
BA seems to be building the appropriate fleet for this type of operation - 787s and A350s - but whether they will be able to exploit their capabilities fully 10 - 20 years from now is an open question.