This question, and variants of it, have been posted before on FT. AFAIK there have still been zero attempts to develop an OTA like this, at least not since the days of EasySabre, which was decommissioned 24 years ago.

I personally believe that this could be profitable as a kind of side business (passive income) as long as overhead costs are kept low enough. Some concerns, though:
* These discounted fares often include zero or almost zero commission. How would you make a profit? Own commission? Membership? Membership own commission? Adding commissions may mean that it becomes cheaper to book on Expedia and lose the sale.
* When you operate an OTA that tickets an itinerary, you will also be the point of contact for the customer if anything goes wrong before travel. Flight cancelations, the passenger getting sick and needing to cancel or rebook, etc. To avoid having to employ a too-expensive 24-hour support team, you would need to enable your customer to manage his booking himself, and this leads us to the main concern:
* How will you avoid a customer issuing tickets or making changes that will result in a debit memo? And how will you handle a debit memo? Will you pass it on to the customer who chose you for the low fare and may refuse to compensate your $3k debit memo that he caused? One of the reasons some cheap options often don't turn up in OTA's is that they are complex itineraries, which carry a higher risk of leading to debit memos, a risk the OTA just doesn't want to take for the measly commission they are getting.

Ultimately, I do believe it can be done and be a profitable side business, but you would need some extremely good industry knowledge and backend programming to avoid debit memos or other costly mistakes. And this may mean you will still need a 24-hr support system if the system isn't sure if something will cause a debit memo.

An agency debit memo (ADM) is a notice sent, normally by an airline to a travel agent, requiring the recipient to pay a sum of money to the sender. A frequent reason for issue of an ADM is where an air travel ticket has been issued and its rules have not been fully complied with, such as where the fare rules require tickets to be issued within three days of creating the PNR or reservation, and the ticket was issued on the fifth day.