Simplifying this circuit using optotriacs?
The short answer is NO.

The circuit you post is already quite simple and clever for what it does. The "optotriacs" suggestion you saw was probably a misunderstanding on how this circuit operates, which was already described in this site.

In OpenTherm/plus communication, the master (e.g. a thermostat) sends data to a slave (e.g. a boiler) by "pulling down" the bus voltage. The slave answers back by changing the bus current. The voltages need to be between specified limits; hence the specific zener diodes.



The diode bridge (4 x 1N4148 diodes) is not absolutely necessary if you know the polarity of the slave, but the OpenTherm specification mandates that X1 and X2 could be swapped, for convenience.

The opto-isolators could also be removed from the circuit, however, you will be connecting systems with different power supplies that do not share a common ground; it is safer to maintain these circuits isolated.

I have seen other OpenTherm interfaces with less components, but they certainly would not be compliant with the OpenTherm spec. A few cheap components will save you from lots of headaches, especially if you do not have an oscilloscope to figure out what does not work. I have also seen other more complicated ones, using op-amps. Or this one using comparators. The one you picked is the design used by the popular OTGW project, it is proven and I recommend that you stick with it.