I'll address some posts-
1. Regarding complexity and break-downs/repairs with this system- I know anything mechanical and surely nowadays with everything computer-controlled, anything can and will break down and need repair. I am extremely confident in the Daikin products (I mean real "legacy" Daikin, not the Goodman line being re-vamped slowly) in that their stuff is extremely high-quality and built to perform as well as last as you would expect. Daikin is not equal to most other "mini-splits" or VRV/VRF type systems other than Mitsubishi. Most manufacturers have brought something to market in the mini-split line and it is showing that they didn't want to fund R&D or be real proud of their product line. It's sad because all the cheaper made stuff will probably give the newer technology a bad name over time. I only considered Daikin and Mitsubishi. I also have a pretty good relationship with a large number of people at Daikin, I feel that they would help me in a time of need should something major arise with a repair.
2. No, you can't install a mini-split/VRV coil over a gas furnace and cassettes/high-wall/fan coils elsewhere. Just no.
3. I wasn't concerned with payback, although my mother will probably live long enough in that house to see the payback of the additional cost over a sub-par, typical residential equipment change out with the energy savings she will see with this system. Payback with a VRV/VRF type system (not a "mini-split") might look like 15 years but when you factor in your comfort and other performance into the equation, payback is a lost thought and you realize how poor performing typical single and two-speed equipment really is.
4. The mini-split and VRV/VRF lines of equipment from most manufacturers have indoor units that look, feel and operate just like your current indoor air handling unit that is in a closet, attic or crawl space with ductwork attached. The installers can remove your existing air handling units and put in new air handling units matched with the condensing unit from the mini-split manufacturer. It's going to be a LOT quieter, tho. Strip heat is not normally needed, even in colder climates. While the condensing units do operate a defrost cycle, many manufacturers have methods to combat the introduction of cold air into the space. Daikin shuts down the evaporator (indoor) fan during defrost. The Daikin VRV-S system I had installed will produce 100°F discharge air at 0°F ambient. You're not going to see that with your Bryant, Carrier, Trane, Goodman or Lennox heat pump.
5. Nobody is getting any HVAC system that is a permanent installation (not a PTAC/Window unit) for $1700. The equipment cost of a simple 2-ton split system is $2,000. You won't get a contractor to show up for less than $2,000. The equipment cost for a 1.5 ton mini-split with a ductless high-wall unit from any reputable manufacturer is $1500+.
6. Yes, repair/etc., with this particular commercial-based system is going to be limited to certain contractors in our area. Out of the 4 contractors that I had show up (I actually sent out invitations/calls to 7, 3 did not respond), only ONE had installed this type of system previously (my friend). All perform commercial as well as residential work ( the same crews with any contractor do not cross-pollenate. There's commercial crews and residential crews. A commercial crew performed my installation.) I am not worried about repair. The contractor that I used, I have developed a relationship with and they are now more eager to try to sell these systems after this installation and actually seeing the performance themselves. With that said, I don't want just any HVAC contractor showing up at one of my properties to perform work because I'm in a tight spot. I want highly experienced and trained people.
As I stated in my OP and stressed, not many people will have much desire to spend the money necessary for a system like this, but anyone who does and can realize all the benefits will certainly say it's worth every penny when done. I'm not trying to sell anything, I'm not getting a kickback nor do I care what you do at your property. I'm simply throwing out some advice and experience to anyone wanting to listen. I have learned over the years that not many people really understand HVAC and that's an understatement. Even the people that try to sound like they do don't understand it all and don't think about many factors.
One of the biggest benefits of a system like this is the unlimited part-load capacity and the real variable speed of the compressor, condensing fan and indoor fan as well as the metering of the refrigerant, which provides minute part-load capacity. I can't stress enough how great this is. Your weather is never the same day to day and hour by hour at times, neither is the heat gain/loss of your structure.
And yes, I eat this stuff up. I'll never consider myself a nerd, but I get all nerded up in HVAC stuff. I love it.