WRT to feeders and diy pp machines. I've thought about it too and personally I think the whole feeder caper is insurmountable for the DIY'ers. I think the best idea if someone is intent on doing a machine is simply to limit themselves to cut tapes and stick vib feeders. So build a really large xy table with a really fast screw and get a crap load of 8mm and 12mm cut tape linear guides machined out of aluminium and mount them down at one end of the table. Doing it that way they may get a couple hundred parts per strip of cut tape laying down on the table which may be good for a run of 100 or so boards before you need to replace the tapes. pulling back the tape covers will be up to the operator to do before running the job. ie no feeders, no fishing sinkers, limited runs of about 100 or so boards.
I strongly disagree that a good DIY feeder is not possible, it just needs some clever design. It's not an inherently difficult thing to do, just needs thought applied to design details.
If you go multi-lane, that helps remove the size constraint as well as making it easier to accommodate different tape widths - standard feeder bank width, different numbers of lanes with just a differemt set of guide rails.
Another factor in keeping the widest possible potential market is machine footprint. A low-end machine is going to spend a lot of time not being used, so if it takes up a lot of space, it is going to be less useful to people with limited space.
Large banks of passive tape rails are not conducive to a small footprint.
Another issue here is you need high mechanical accuracy in the placement area but not in the feeder/pick area, so by needing to enlarge the table size just to accommodatae feeders, you are paying for precision over a wider area than is strictly necessary in terms of mechanical precision.
This is one reason I like the SCARA arm approach as it has a small footprint & makes efficient use of space. Although it has an irregular reach area, this can be efficiently used by placing feeders, toolholders and reject bins in the outlying odd-shaped areas of accessability.