Unfortunately, TUI have absolutely no interest in expanding. At least in the short-term...
They're viewing this winter as a time to 'stabilise the operation' and, imho as a money pot for their yields... Up the revenue on their current seats before adding more.
Seems the business has a rigid and inflexible structure, they're not willing to lease in capacity and are sticking with their plans to retire some of the 757s allowing for the 737s to take up the void through the rest of W19. They're currently hoping for the return of the MAX fleet by February 2020. What happens if the MAX isn't flying by then is anyone's guess.
The company is 'vertically integrated' in order to control most aspects of it's own supply chain. This great for maintaining a cost base, but turns the company into a sluggish goliath when it comes to being agile and flexible to market changes. This is where Jet2 will make a killing.
In a nutshell, Vertical Integration can be seen like this:
Marketing > Flights > Destination Services > Content (Hotels/Cruises)- TUI Marketing is heavily involved with pushing the TUI 'Brand Strategy'. This is centred around advertising a TUI holiday on a TUI flight with a TUI hotel, etc.
- TUI Airways won't add flights a request from the Tour Operator, even without the MAX groundings, TUI remains focused on retiring older 757s through W19, allowing 737s to pick up the flack (they currently expect the MAX to return by Feb 2020). So even if capacity was available, TUI Airways are powerless to use it without the Tour Operator.
- TUI Destination Services would need to either increase presence in current markets or open up new offices to establish a presence, this would involve contracting transport/transfers/service/handling/excursions and represents a significant cost.
- TUI Tour Operator won't contract 3rd party hotels as they're heavily invested in their 'own' brand hotels/cruises (TUI Blue, RIU, Family Life, Marella, etc).
In the end, TUI are seeing the demise of TCX as a god send for their profit margins and not as an opportunity to expand further into different markets, at least not in the short term... Expansion will happen eventually, but this will be at the 'standard' slow/steady pace that TUI has always worked to.