I think I need an additional instrument for live performance which will cover areas Tempest can't do - effects, sampling, mixer with 1 - 2 stereo inputs, of course, more memory and normal MIDI CC control of parameters. Basically "more synth/sampler than drums" oriented groove box. There are Elektrons, but for some reason, I don't like their interface and sound too much.
I friend of mine just bought Prophet X, and I really like X's sound, all the options etc. It's quite a fresh concept, and all the modulation options now give a truly modular experience. There's only need in good analog style sequencer with resets, assignable modulation lines... So a new tabletop machine based on X engine could be amazing.
Plus yes - another killer possibility is to invite Dave Rossum and implement at least some features of his new Assimil8or Phase Modulation sampler and Morpheus Filter. They sound completely out of this world (I mean the quality at the first place ). I don't have Eurorack (use old Frac modular rack and don't want to start with Euro ) so if such a machine exists I would order it in a second, even with the price tag close to X.