I would agree TDK - what would be the point, they have made every effort to pull out of regional operations in recent years - they have their domestic flights into Heathrow (whenever i fly on one they are close to or are full) to serve London and their onward connections.
Iberia with Iberia express is operating in a different market (although i would have thought just buying out the rest of Vueling it doesnt own might have been easier if possible vs setting up another airline and dealing with the cost of industrial disputes) - its a bigger country land mass with more airports to cover over a wider area, there are islands to feed and serve, and they have more competition in their home turf domestic wise from their main bases - BA at present has no competition domestic from LHR and from LGW whilst there is some competition on domestic - it owns part of one of them - Flybe. As for the near europe - Easyjet covers that cheaper alternative (along with a slew of other airlines ) at LGW and BMI itself tried cheaper product offering at LHR and it didnt work.
Notwithstanding all of this - BMI Regional have the wrong aircraft for any major impact at LHR and WW have the wrong fleet mix for BA at LHR (LGW - maybe!)
If VS did get the slots I am sure they would want brand new aircraft and style it like Virgin America - why bother buying an airline with the wrong setup for the job - although in my honest opinion the limitations of where they can fly to and lack of possibility to easily expand - i can only see this as a big P&L cost to them.