v17.2 WHDLoad brings support for quitkey feature which require presence of HW instruction not provided in ACA500's onboard CPU. Let's say it puts ACA500 close to stock A1200 from HW preconditions of speed, instruction and part of chipset. It won't help preload case study you brought up. Vanilla, unmodded A500 Rev6-7 comes with 0,5M chip and 0,5M trapdoor which can be translated to 1M chip and that leaves some 1,5M fast for preload if you practice MAPROM. That amount is enough for 2-disk games. If you omitt MAPROM, there's space for 3rd disk. Effectively, you get scope narrowed down to 4-disk game installs and that put your personal preference above the device/platform general functionality. In plain words, your needs surpass targeted market segment for ACA500.
Elbox 68030 might be solution for your case, if they commit and build one for sale. Personally, I wouldn't hold my breath for this one; ACA500 was delayed for at least one year after announcement and that comes with alongside upfront and detailed communications between IC and community. I don't expect any more details outside already published ones, including price without VAT. If you have no critical preference towards internal/external implementation, I'd advise to check ACA1232 33/40 versions which can attach to ACA500 and are selling.