Some interesting ideas so far so thanks to everyone for their comments.
A couple of points I would like to say for future posts, as this is already a very complex project already and even after 4 pages there are some major distractions in the discussion which confuses the relevant messages I need to consider. So please when posting ask yourself if your comments are directly related to my project or a completely unrelated product, in which case you should probably start a new thread about it

OK I will try to address everyone's individual concerns or suggestions.
1. If you think of it from the point of view of I am going to do a bespoke cased system for myself and if anybody else likes it I could supply suitable case parts or certain interfaces e.g. the joystick/mouse 9pin adaptors. I am not necessarily starting a business here as such. I just KNOW that C=USA's effort is so pathetic I could do better. How much it will cost me to make one for myself I don't know but I know it IS possible to do much better.
2. The cases - there is no particularly difficult case to replicate but each case requires a lot of work by me to give to another party to produce. So for this reason I thought of what I thought was the most difficult to replicate. End of the day if we had some replica cases made up it comes down to quantity of solid orders with non-refundable deposits. So if 50 people wanted an A500 case that's fine, it's not limited to which case designs I personally like or AIO/3 box design only.
3. A few people have commented on PPC or FPGA systems. I am not going to start getting involved in purchasing such esoteric hardware but if for example the PPC boards can be accommodated in the case as far as size goes I have no problem with this.
4. The AROS thing, there has been a comment inferring I am just going to freeload off the AROS team. Firstly you don't know me so why assume the worst? Secondly it was just an idea but I did state I wanted an AROS BIOS system so obviously if AROS was to be factored into the hardware parts list I would have to forge relationships with people working on AROS. Finally if this was a business and I was selling such machines with the system pre-installed I would happily donate to AROS bounties etc, although If I was donating 10% of profits to AROS I would expect a say in for example what order new drivers are written in.
5. Case materials - I want to make a plastic cases for the AIO designs for sure. The A1000 was plastic too so see no problem with that either. Things like the A2000 style would have to be metal with a plastic front end. I don't believe you can replicate a shape with various slats and creases well using metal personally. I don't know how it will be done, the experts in the field or prototyping cases would decide exactly which process to use and which materials. 3D printing however does not produce a case you can use without a lot of labour intensive finishing so it will not be a 3D printer used. I still need to discuss this with a few companies anyway and I am nowhere near being able to comment on how this should be done yet. As soon as I contact these people they will want some technical designs to quote on too so this is a slow burn project so please bare that in mind
6. It may be that I don't use AROS anyway and just stick to Windows. It would be nice to have AROS but I am no expert on that OS at all (or anything NOT Windows based to be honest) so we shall see. The main focus is to produce something that looks nothing like what is off the shelf now (like Cybernet ZPC range etc) and something close to an original Amiga. I said quite honestly up front if this is not what you are looking for you won't be interested in what I build. However you may well ask me how did I make that case and how much would it cost to produce say 10 more for some members here.
7. Keyboards, obviously the ideal is an actual Amiga keyboard with only 10 F keys and only two keys above the cursor T block of keys in the middle. This would be nice and certainly expected on a $1500 machine but to be fair it's not like it's massively different to PC keyboards today, the Atari ST had bespoke rhomboid F keys and that I could understand but from a distance you wouldn't even know. Who knows what the future holds but like I said I am building something unique but if others want parts reproduced from any aspect of what I have done I am happy to sort that out. I have not set out to start a big business with offices etc over this. It's still just a little hobby project at this stage I hope others will find interesting.
8. The joystick adaptors, right these are something I am either going to purchase (I remember seeing them for €40 for two ports and they interface via standard USB headers) OR I will make them myself using some specialist parts and a soldering iron

They don't need any drivers at all as they are not mapped to keys on the keyboard as Keyrah does it. As far as Windows is concerned a new joystick just got plugged into the USB port.
9. I want to put i7 based motherboards inside the machine I am building, however there are a couple of issues. The boards will no have any kind of PCI cards on them so the onboard GPU must be Nvidia or ATI and it must be of a very reasonable speed. Maybe AMD Phenom II would work out better I don't know yet. But the form factor more than likely will be Micro ATX. I don't like the way the interfaces will work out there on the back of the machine, there would be a lot of blank solid plastic apart from the 6x2 inch block of connections on the motherboard.
I think I have covered everything relevant so far, prod me if I've missed your question

If you think of this project first and foremost as being on to investigate the viability of making A1200-a-like (or other Amiga) cases in plastic today and nothing else you won't go far wrong.
What I will add is yes this project would be massively more simple and faster if I just used existing parts, but this is simply not sustainable, how many empty A1200 or A500 cases are around etc. I might do something like that with Keyrah as well though just for myself but I know full well that only a handful of people would be able to do that after me as the cases are hard to come by so this is of little interest to everyone.
What I am trying to find out from Amigans is what they would choose given the specs/restrictions.