Eleri was on tv again recently, in a documentary aboout TV prsenter Alex Jones. At the moment the programme (in Welsh) Alex Jones: Y Fam Gymreig is available on S4C's replay website clic.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.