You'll never raise the money to make a 5v tolerant ASIC. We would be taking hundreds of thousands of dollars.
You'd have to use a CPLD/FPGA. But you may as well recreate the whole Amiga.
Add to that, too few Amiga users have an Amiga which uses a buster chip. A3000 / A4000.
This would have to be a hobby project, labour of love.