Upper RF limit in discrete design
I'm not sure the "RF stuff" is the limit.

How about 32/33 prescalars, certainly an untuned circuit? 

You can build frequency-multipliers (X2, X3) as needed to reach higher frequencies, but can you get power gain? 

As long as you have some non-linearity, you've got a mixer for UP or for Down conversion.

I've built S-band (1.2GHz) oscillators on my workbench, on Rogers Duroid, with about 2" stripline hanging on the emitter of a micro_T transistors.

If you want a quality oscillator, you mount the active device atop the resonator (stripline or cavity or ceramic ball)

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Motorola had micro_T transistors with 4+GHz Ftau, the ceramic body being 3mm across, 40+ years ago. Who knows what they could provide for SPECIAL CUSTOMERS?

For 30GHz resonance in air dielectric (so we know the precise size needed), the wavelength is 1cm; quarter-wave is 2.5mm. Is a cavity better?

Thus working with BARE DIE may be needed. Not sure BareDie count as Discrete.

If you can bond the Emitter to a Resonator quarter_wave, with a varactor die bonded to the other end for tuning, we may have something.

I would think the Electronic Warfare people have long pushed the frontiers of what is possible, in building monitoring equipment that supports AVOID SURPRISES.