I have two ideas to simplify TX and RX:
1) Use STCS05A https://www.st.com/resource/en/datasheet/stcs05a.pdf
as 0,4A current-limiting TX switch. So the TX would be STCS05A (1€) + 4148 diode + 7V5 zener diode (dropping bus DC voltage by 7V, as specified for TP1-256 Transmitter).
2) Use MCU with integrated DAC and comparator (COMP). Positive input to COMP will be the BUS voltage divided by resistor voltage divider (to fit 3,3V COMP's rail-to-rail voltage). Negative input will be a reference voltage provided by internal DAC. COMP output will trigger capture channel of the timer in the same way as RX made of discrete components. DAC reference voltage may "follow" (calculated and controlled by software) the EIB_DC voltage measured by integrated ADC. So the RX would be actually made by only four resistors (the bus voltage divider and the DC voltage divider).