I don't think it's an issue, depending on the non-conforming areas. An isolated engine such as VP does on the MD22 series is an advantage. Bonding only increases electrolysis..
If bonding cables are intact and end at an anode all the bonded parts cannot suffer any 'electrolysis' because the anode will protect all metals in the bonded circuit. One will not find Volvo recommending not bonding the motor even on their electronically isolated motor setups. Bonding underwater metals simply does not (cannot) increase a risk of corrosion. For sure bonding cable failures ignored are a threat - and even more so with poor alloys in the string.
I think some ABYC requirements are stupid. Examples: Bonding thru-hulls to electrical ground. Dumb. Isolated is better. Or not allowing a fuel drain petcock at the bottom of a tank. Stupid. Drain valves can be backed up by threaded caps for redundant closure, and if it was easier to drain water/sediment it could save many boats from engine failure in a seaway resulting in disaster and/or close calls that put crews at risk.
Bonding fastened to the all-ship-negative just means the shaft anode(s) are taking up protection of the bonded collection. Hence better to have a separate anode for the bonded collection.
Thru-hulls - bonded or not - have nothing to do (neither galvanically or corrosionally speaking) with fuel tank drains or any other part of the fuel system for that matter.
Agree with your view that with high grade (85 5 5 5) through hulls there might be little reason to engage in bonding because they are already very corrosion resistant particularly in fiberglass hull (not necessarily a good choice in a metal or wood hull by the way.) But that still depends on whether you are in marina or not. Either way bonding makes very good sense and - and cannot possibly hurt - no matter the grade of the underwater metals.
Bonding traps stray current - the kind that your own boat produces which is the usual case -- don't discount its utility.
Charles
