I was wondering if it would be at all possible to put the ECS/AGA custom chips onto a pci card in a similar fashion to what the Hard SID / Catweasel MK3 have done for the c64 chips?
Yes, it would. But why?
I really can't see a need for such a card. It would be bloody expensive to develop and IMHO not many people would buy it as there really is no need for it. I wouldn't for sure.
If it is possible, this would be excellent for both AROS/Amithlon/UAE and AOS4/Morphos.
Again why? Neither OS4, MorphOS nor AROS needs it, and Amithlon/UAE is emulating the chipset in software. I'm not buying brand new PPC hardware anyway to run old aga apps.