There is much talk at present on a closer harmonisation of mainline and TOM. One rumour doing the rounds is that pilots will be either 73/75 or 75/76. BALPA are working on closer alignment of T&Cs so the general shift seems to be to a single entity.
Some TOM Capts are ex (relatively) junior Mainline FOs. They are at TOM for 5 yrs min with the option to return if there is a place. This may sting a bit because it may turn out that a TOM Capt would look to return to the Mainline fleet but find that guys senior to him are still FOs. The Senirity List is already a common one for both.
The logical (?) extension to all of this would be fleets as above, common senoiority, T&Cs (less some aspects such as pension) and A/C rostered to suit the thickness of the city pair route, regardless of callsign. So, a Mainline flightdeck with TOM CC on a Mainline 75 flying a TOM route? Who knows?
Ops for all of TUI is based in HAJ.