The Artisan Electronic Instruments Trentasette remains a real possibility. AEI offers both keyboard and module versions with MIDI In/Out, and that means - aside from keyboard length - this combination checks nearly all the boxes. The instruments look sharp, with lots of wood trim, and they sound quite good. Plus, the prices are very reasonable ($1050 and $775). But this is a genuine boutique company. Instruments are made to order.
The Trentasette has an Baroque sound engine with a three-octave vel-sense keyboard:
Monophonic synthesizer with 25 knobs and 15 buttons to get at that sound fast, and all savable for instant recall.
Dual Analog Oscillators with PWM and Shape Modulation from Saw, through Blade and Triangle waveforms.
Additional Digital PWM Oscillator/Noise Source
Advanced CMOS Ring Modulator with 9 Wave Mangling Variations
Dual Sub Oscillators: -1 or -2 down, Smooth or Square Wave
4 Pole Analog Low Pass Filter with Resonance control into self-oscillation; playable over 5 octaves.
Analog VCA
4 rate modulatable LFOs with 8 waveforms and 4 modes of operation, including key-sync and one-shot
4 DAHSDR (ADSR plus delay and hold) with Looping and 3 trigger modes.
2 8-Step Modulation Sequencers. (special ADSR mode)
MIDI Clock sync on ADSRs and LFOs
7 Modifier Functions allow combinations of Modulators and/or Keyboard inputs to create all new modulations.
21 Modulation sources routable to 18 Destinations for complex sound generation possibilities.
60 Patch Storage and Recall with 10 perfomance Quick Access buttons.
Analog Sound...Digital Stability; all Through-Hole parts
Assembled by Hand in the USA
Website:
https://www.artisanelectronicinstruments.com/[Update: I just learned from AEI that they would be willing to custom build a four-octave keyboard for the same instrument.]