The move to QC will be
nothing like the 32->64 bit transition.
Infact the move to 64 bit is quite painless.
If you are running a 64 bit OS on intel/amd then you have the flexibility of running 32-bit software (at full speed with no performance penalty) or 64-bit software where needed.
Software that doesn't require 64b capability can be expected to perform slightly worse if compiled as a 64b app and this holds true for other architectures too.
The key point here is that 32b software can happily co-exist with 64b software on a 64-bit OS.
Now, QC with its qbits and other jargon is beyond my grasp but I have a feeling that code for QC software will look
nothing like what we have today and thats the scary bit.