Originally Posted by
sefrischling
PSA did this with their L-1011 to some extent, with a lower deck lounge. the only airline that would attempt this is VS, outside of that the costs of this are far to expensive.
PSA was the only airline to have a lounge in underbelly, but there is a plenty of experience with lounges on upper deck (747) and main deck (DC-10, A340-600...). However, seats seem to sell better. Qatar has a first class lounge on A340-600, but they declare that they plan to replace it with business seats. Singapore has common spaces on A340-500, both in executive economy (very rear) and business, but their new all business interior does not seem to feature them.