I agree the idea of the airflow system would be wonderful....but the PRICE !!!
I have a Frister Rossman that I bought about 5 years ago. The base opens up completly showing all areas so threading is reasonably easy. In honesty I wonder how often people change their threads....If I need to change the threads I take off all tension and cut the threads and tie small knots from the new colour thread and feed through the feeders then I just have to thread the needles. I reckon that takes me the whole of two minutes.
I also do dressmaking and some upholstry so use it regularily....I even put in zips and piping.
Mine cost £250 which is about $360..........
If I was paying $3000+ it would have to make me breakfast in bed for at least a year as well !
My honest advice is to anyone looking at getting a serger is see if anyone will let you have a go first....the speed on these things can be pretty intimidating and not for everyone.... which brings me to the footpedal. I'm not so sure that a start stop button would make me feel totally happy as I would have to take my hand off the fabric to press the button to stop.....as it has a cutting blade it would be really easy to go through just that bit more fabric than you wanted.......anyway these are just personal thoughts but I hope they might help.