What is the maximum frequency of CMOS (3.3V) level triangle (or square) wave that I can achieve with serial discrete ICs (for example: discrete PLL or DAC + OpAmp cascade)?
This depends on multiple factors on the components you choose that you can find in the datasheets of the components. Some examples in the case of CMOS are the on and off times (rise and fall time) that can give you an insight on how fast the mosfet can go to 3.3v and 0v and the capacitances around the mosfet which in higher frequencies can act as filters.
In the case of Opamps the slew rate is the most important along with the bandwidth of the op amp which sets the limits on the product of frequency * gain.
I guess there's well performing GHz range transmitters which can well output for ex. the needed voltage, the limit is at the receiving end. Different CMOS cicuits need differently wide pulse to do their jobs. Check how wide pulses your circuits need, multiple it by 2 and calculate the inverse. That's your frequency.