I've developed over 25+ LN apps (kriptode.com) and still have so many ideas, take your pick, tip me when you're rich.

Breed LN nodes Use https://vls.tech to create nodes, get them to top spot on routing charts and then sell them via escrow

Predict tweets - find alpha https://twitter.com/samuel_spitz/status/1581814522624430080 People that discover viral tweets get paid. Others get access to tweets first. Bet on tweet virality to win

Ultrasonik payments Add to lnbits payment plugins https://charliegerard.dev/blog/ultrasonic-payments/

hosted lnbits with %0.5 fee - undercut opennode! automate everything

lnurl-w with captcha to deter automation - find a way, pow or something more abstract?

Bonus: LN app idea thread from voltage ceo: https://twitter.com/gkrizek/status/1567919285393047553