And using VHDL to develop silicon would not be the optimal way to design an ASIC.
It's only how a lot of companies actually do their work. Even AMD's Bobcat x86-64 core is VHDL - yeah, it costs them some potential clock speed, but the benefits outweigh the downsides for them. ARM cores are designed in VHDL as well. I expect a lot of other cores are - CPU, GPU, etc. Designing custom silicon these days needs a lot of resources. Anyway, who would care, Natami/FPGAArcade Minimig as custom silicon would run very fast even if made on an ancient 250nm process.
Edit: Must reiterate that it would still be very costly and highly unlikely to happen, hence the FPGA solutions which will still end up thrashing a classic Amiga into the ground in terms of performance and features - and at least the hardware can be updated with bugfixes! We can all hope a Chinese knock-off company makes an Amiga-in-a-joystick ASIC one day that we can hack apart like the C64-in-a-joystick :-)
Btw, Franko - I don't think that Natami will be 100% compatible with classic Amiga software, especially demos and games that really hit the hardware and do timing incorrectly (assume 68k clocks, rather than use hardware timers, etc). Maybe there will be an A500 level core developed in due course to allow that, but don't expect it out of the box.
