ST6210 can source 15mA by any pin, thus 3 fused pins can source around 45mA which is enough to drive BTA16. This circuit can work, but the fact is there should always be an isolation between high voltage side and low voltage side. Or it will not be safe to operate. Your MCU can be blown out if any short circuit happens, and also any human operator can get a nasty shock. So an optoisolator is always recommended. If you don't want to use any optoisolator for zero detection, you can use a resistor divider, followed by a zener diode.