My A500 setup is an amazingly fun Amiga...
If it wasn't for the crazy expense, I wish everyone could do this 
I already have a rock solid PSU,
Independent regulation on each supply rail
First order LC (film) filtering on +5V@10A rail
On the latest revision, I separated the audio power from system power.
I'm now getting the audio +/- 12V from a separate pair of +/-15V SMPS and using Analog Devices highest quality precision linear regulators to step that down to +\- 12V through a second order LC (film) filter, exclusively for Paula's audio out amplifier circuit.
Those two linear regulator IC's alone add over $30 CDN to the PSU BOM
I don't really hear the difference of course... but It's 'impressive' (maybe that's not the word) to burn this much effort and money in the name of audiophilia ... for 1980's digital sound... 
The mains power switch is an NKK on-off-mom rocker switch, so when I use this same PSU design in my A2000, I now have soft-power-on-off without the need to bodge an ATX style power button to the case.
All supply rails are monitored and the monitor IC controls the fan, will shutdown the PSU in over-voltage, over-current, over-temp conditions using the primary SSR and logs performance and reports out to the Amiga via I2C
Such a power supply would need too many quality and feature compromises to make it cost effective for commercial production.
And I think I know your mind well enough...
You'd not want to go to production with something if you couldn't have the best offering... 
Making a better version of the 100pin riser board with a Buster socket or Bluster CPLD, buffer ICs and Zorro II RC termination would be great.
I could see paying ~$200 CDN for such a board.
I imagine a fair number of the Checkmate case purchasers would opt to upgrade to that, especially as we could then have two Zorro slots (case supports this) and not just one 100pin slot.
I don't think I'm the guy to round them all up though and get them to pool their money.
Also... not entirely sure that this alone would resolve my OP.
I'll just leave this post up, in case anyone else spots an issue with their Gotek in the ACA500plus & ACA1234 accelerator in a Checkmate case... And If I find a fix on my journey, I'll post that too.