I would like to see British Airways BA merge with Swiss LX because both markets are sufficently distant to make synergies work with limited cannibilization of markets.
Both brands are considered to be premium brands (Swiss recently won "Leading Airline of Europe award") and Zurich ZRH would be a great addition to Heathrow LHR as a hub due to ZRH's central european location and reduce congestion at LHR. Zurich has alot of capacity to spare (Terminal B empty) and will have a new in airport shopping center within the next few years (airside center). Switzerland also has a relatively high percentage of premium traffic and when Swiss finishes unloading the MD-11s (Swiss as a company was never really satisfied with these birds) the fleet will be one of the youngest in europe and with a premium product in all classes.
Already Swiss' Travel Club Frequent flyer programme is being merged with BA's Executive club (I'm Travel Club Silver and I'm not too excited about BA's executive club terms).
Three dents in the plan: BA doesn't operate widebody Airbus, but I think the other factors can overcome this; Swiss' precarious financial position; and lastly LHR terminal 5 when it comes online will increase capacity at LHR (though not sure how this would increase landing slots). Personally I prefer flying through ZRH then LHR because ZRH is easy to navigate and get around quickly whereas LHR is a mini-trip in a trip.
Though I would like to see Swiss exist on it's own, it would be too difficult to survive against the european majors, especially if a merger frenzy is about to begin (step 1 KLM- Air France).