Hi lukaszadrapa,
For the moment there are no plans to add Matlab/Simulink support for MPC5748G. Instead we are committed to add Gateway products support in Matlab/Simulink for the next generation of NXP's S32 Processing Platforms.
Nonetheless, the actual MPC5744P support could be deployed with a few tweaks on MPC5748G for the existing peripherals if the customer is interested in automatic code generation.
Hope it helps!
Daniel